Nucleic acid sequences encoding capsaicin receptor and capsaicin receptor-related polypeptides and uses thereof

ABSTRACT

The present invention features vanilloid receptor polypeptides and vanilloid receptor-related polypeptides, specifically the capsaicin receptor subtypes VR1 and VR2 (VRRP-1), as well as the encoding polynucleotide sequences. In related aspects the invention features expression vectors and host cells comprising such polynucleotides. In other related aspects, the invention features transgenic animals having altered capsaicin receptor expression, due to, for example, the presence of an exogenous wild-type or modified capsaicin receptor-encoding polynucleotide sequence. The present invention also relates to antibodies that bind specifically to a capsaicin receptor polypeptide, and methods for producing these polypeptides. Further, the invention provides methods for using capsaicin receptor, including methods for screening candidate agents for activity as agonists or antagonists of capsaicin receptor activity, as well as assays to determine the amount of a capsaicin receptor-activating agent in a sample. In other related aspects, the invention provides methods for the use of the capsaicin receptor for the diagnosis and treatment of human disease and painful syndromes.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/978,303, filed Oct. 15, 2001, now U.S. Pat. No. 6,790,629, which is acontinuation of U.S. patent application Ser. No. 09/235,451, filed Jan.22, 1999, now U.S. Pat. No. 6,335,180, which application is acontinuation-in-part of: 1) U.S. provisional patent application Ser. No.60/072,151, filed Jan. 22, 1998; and 2) U.S. patent application Ser. No.08/915,461, filed Aug. 20, 1997 now abandoned; and 3) PCT internationalapplication PCT/US98/17466, filed Aug. 20, 1998, each of whichapplications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to nucleic acid and amino acid sequencesencoding a receptor for vanilloid compound and polypeptides related tosuch vanilloid compound receptors, and to the use of these sequences inthe diagnosis, study, and treatment of disease.

BACKGROUND OF THE INVENTION

Pain is initiated when the peripheral terminals of a particular group ofsensory neurons, called nociceptors, are activated by noxious chemical,mechanical, or thermal stimuli. These neurons, whose cell bodies arelocated in various sensory ganglia, transmit information regardingtissue damage to pain processing centers in the spinal cord and brain(Fields Pain (McGraw-Hill, New York, 1987)). Nociceptors arecharacterized, in part, by their sensitivity to capsaicin, anatural-product of capsicum peppers that is the active ingredient ofmany “hot” and spicy foods. In mammals, exposure of nociceptor terminalsto capsaicin leads initially to the perception of pain and the localrelease of neurotransmitters. With prolonged exposure, these terminalsbecome insensitive to capsaicin, as well as to other noxious stimuli(Szolcsanyi in Capsaicin in the Study of Pain (ed. Wood) pgs. 255–272(Academic Press, London, 1993)). This latter phenomenon of nociceptordesensitization underlies the seemingly paradoxical use of capsaicin asan analgesic agent in the treatment of painful disorders ranging fromviral and diabetic neuropathies to rheumatoid arthritis (Campbell inCapsaicin and the Study of Pain (ed. Wood) pgs. 255–272 (Academic Press,London, 1993); Szallasi et al. 1996 Pain 68:195–208). While some ofthis-decreased sensitivity to noxious stimuli may reflect reversiblechanges in the nociceptor, such as depletion of inflammatory mediators,the long-term loss of responsiveness can be explained by death of thenociceptor or destruction of its peripheral terminals followingcapsaicin exposure (Jancso et al. 1977 Nature 270:741–743; Szolcsanyi,supra).

Responsivity to capsaicin has been used to define sensory afferentfibers that transmit signals in response to noxious stimuli (chemical,thermal, and mechanical stimuli); however the precise mechanism ofaction has remained unclear. Electrophysiological (Bevan et al. 1990Trends Pharmacol. Sci 11:330–333; Oh et al. 1996 J. Neuroscience16:1659–1667) and biochemical (Wood et al. 1988 J. Neuroscience8:3208–3220) studies have clearly shown that capsaicin excitesnociceptors by increasing plasma membrane conductance through formationor activation of nonselective cation channels. While the hydrophobicnature of capsaicin has made it difficult to rule out the possibilitythat its actions are mediated by direct perturbation of membrane lipids(Feigin et al. 1995 Neuroreport 6:2134–2136), it has been generallyaccepted that this compounds acts at a specific receptor site on orwithin sensory neurons due to observations that capsaicin derivativesshow structure-function relationships and evoke dose-dependent responses(Szolcsanyi et al. 1975 Drug. Res. 25:1877–1881; Szolcsanyi et al. 1976Drug Res. 26:33–37)). The development of capsazepine, a competitivecapsaicin antagonist (Bevan et al. 1992 Br. J. Pharmacol. 107:544–552)and the discovery of resiniferatoxin, an ultrapotent capsaicin analoguefrom Euphorbia plants that mimics the cellular actions of capsaicin(deVries et al. 1989 Life Sci. 44:711–715; Szallasi et al. 1989Neuroscience 30:515–520) further suggest that the capsaicin mediates itseffects through a receptor. The nanomolar potency of resiniferatoxin hasfacilitated its use as a high affinity radioligand to visualizesaturable, capsaicin- and capsazepine-sensitive binding sites onnociceptors (Szallasi 1994 Gen. Pharmac. 25:223–243). Because avanilloid moiety constitutes an essential structural component ofcapsaicin and resiniferatoxin, the proposed site of action of thesecompounds has been more generally referred to as the vanilloid receptor(Szallasi 1994 supra). The action of capsaicin, resiniferatoxin, and theantagonist capsazepine have been well characterized physiologicallyusing primary neuronal cultures (see, e.g., Szolcsanyi, “Actions ofCapsaicin on Sensory Receptors,” Bevan et al. “Cellular Mechanisms ofthe Action of Capsaicin,” and James et al. “The Capsaicin Receptor,” allin Capsaicin in the Study of Pain, 1993 Academic Press Limited, pgs.1–26, 27–44, and 83–104, respectively; Bevan et al. 1990, supra).

The analgesic properties of capsaicin and capsaicinoids are of muchinterest for their uses in the treatment of pain and inflammationassociated with a variety of disorders (see, e.g, Fusco et al. 1997Drugs 53:909–914; Towheed et al. 1997 i. Arthritis Rheum 26:755–770;Appendino et al. 1997 Life Sci 60:681–696 (describing activities andapplication of resiniferatoxin); Campbell et al. “Clinical Applicationsof Capsaicin and Its Analogues” in Capsaicin in the Study of Pain 1993,Academic Press pgs. 255–272). Although capsaicin and capsaicin relatedcompounds can evoke the sensation of pain, cause hyperalgesia, activateautonomic reflexes (e.g., elicit changes in blood pressure), and causerelease of peptides and other putative transmitters from nerve terminals(e.g., to induce bronochoconstriction and inflammation), prolongedexposure of sensory neurons to these compounds leads to desensitizationof the neurons to multiple modalities of noxious sensory stimuli withoutcompromising normal mechanical sensitivity or motor function, andwithout apparent central nervous system depression. It is this finalphenomena that makes capsaicins and related compounds of great interestand potential therapeutic value.

Despite the intense interest in capsaicin and related compounds andtheir effects upon sensory afferent, the receptor(s) through which thesecompounds mediate their effects have eluded isolation and molecularcharacterization. Thus, the development of elegant systems for screeningor characterizing new capsaicin receptor-binding compounds, or foridentifying endogenous, tissue-derived mediators of pain and/orinflammation, have been severely hampered. To date the only means ofassessing the activity of compounds as capsaicin receptor agonists orantagonists has been to examined their effects on sensory neurons inculture or in intact animals. The present invention solves this problem.

SUMMARY

The present invention features vanilloid receptor polypeptides andvanilloid receptor-related polypeptides, specifically the capsaicinreceptor and capsaicin receptor-related polypeptides, as well asnucleotide sequences encoding capsaicin receptor and capsaicinreceptor-related polypeptides. In related aspects the invention featuresexpression vectors and host cells comprising polynucleotides that encodecapsaicin receptor or capsaicin receptor-related polypeptide. In otherrelated aspects, the invention features transgenic animals havingaltered capsaicin receptor expression, due to, for example, the presenceof an exogenous wild-type or modified capsaicin receptor-encodingpolynucleotide sequence. The present invention also relates toantibodies that bind specifically to a capsaicin receptor polypeptideand/or capsaicin receptor-related polypeptide, and methods for producingcapsaicin receptor and capsaicin receptor-related polypeptides.

In one aspect the invention features a method for identifying compoundsthat bind a capsaicin receptor polypeptide, preferably a compound thatbinds a capsaicin receptor polypeptide and affects a cellular responseassociated with capsaicin receptor biological activity (e.g.,intracellular calcium flux).

In another aspect the invention features a method for detecting avanilloid compound in a sample, where the vanilloid compound hasactivity in binding a capsaicin receptor polypeptide, by contacting asample suspected of containing a vanilloid compound with a cell (e.g, anoocyte (e.g., an amphibian oocyte) or a mammalian cell) expressing acapsaicin receptor polypeptide and detecting an alteration of a cellularresponse associated with capsaicin receptor activity in the capsaicinreceptor-expressing host cell. Preferably, the cellular responseassociated with capsaicin receptor activity is an alteration ofintracellular calcium levels in the capsaicin receptor-expressing hostcell. The method can be used to detect vanilloid compounds in samplesderived from natural products (e.g., natural product extracts) or can beused to screen candidate compounds for use as analgesics (e.g, vanilloidanalogs, therapeutic antibodies, antisense oligonucleotides, capsaicinreceptor-encoding nucleotides for replacement gene therapy),flavor-enhancing agents, etc.

Yet another aspect of the invention relates to use of capsaicin receptorpolypeptides and specific antibodies thereto for the diagnosis andtreatment of human disease and painful syndromes.

In another aspect the invention features transgenic, non-human mammalsexpressing a capsaicin receptor-encoding transgene, and use of suchtransgenic mammals for use in screening of candidate capsaicin receptoragonist and antagonist compounds.

A primary object of the invention is to provide isolated polynucleotidesfor use in expression of capsaicin receptor and capsaicinreceptor-related polypeptides (e.g, in a recombinant host cell or in atarget cell as part of organochemotherapy) and for use in, for example,identification of capsaicin receptor-binding compounds (especially thosecompounds that affect capsaicin receptor-mediated activity).

The invention will now be described in further detail.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows the putative domains present in the capsaicin receptoramino acid sequence. Open boxes delineate ankyrin repeat domains; blackboxes indicate predicted transmembrane domains; and the grey boxindicates a possible pore-loop region. Bullets denote predicted proteinkinase A phosphorylation sites.

FIG. 1B shows the predicted membrane topology and domain structure ofthe capsaicin receptor. Open circles labeled “A” denote ankyrin domains;black areas denote transmembrane domains; and the grey shaded areaindicates a possible pore-loop region. “i” and “o” denote the inner andouter membrane leaflets, respectively.

FIG. 1C shows the alignment of the capsaicin receptor VR1 with relatedsequences. Identical residues are darkly shaded and conservativesubstitutions are lightly shaded.

FIG. 2 is a current trace of whole cell voltage clamp analysis ofcapsaicin receptor-expressing HEK293 cells.

FIG. 3 is a plot of the voltage steps (400 ms) from −100 mV to ±40 mVfor the data presented in FIG. 3.

FIG. 4 is a graph illustrating the current-voltage relationship of thedata from FIG. 4.

FIG. 5 is a graph of the voltage generated across membranes ofrecombinant capsaicin receptor-expressing cells when exposed tocapsaicin and tested under conditions of varying ionic compositionsa=NaCl; b=KCl; c=CsCl; d=MgCl₂; e=CaCl₂.

FIG. 6A through FIG. 6F are graphs showing the effects of extracellularcalcium upon capsaicin-induced current in whole-cell voltage clampexperiments.

FIG. 7 is graph illustrating the single channel behavior ofcapsaicin-induced current in capsaicin receptor-expressing HEK293 cellsusing outside-out (O/O) and inside-out (I/O) patches.

FIG. 8 is a graph showing the current-voltage relationship of the dataobtained in FIG. 7.

FIG. 9A is a graph showing the effects of capsaicin and resiniferatoxinupon current in whole-cell voltage clamp experiments in Xenopus oocytesexpressing the capsaicin receptor. Bars denote duration of agonistapplication. Membrane currents were recorded in the whole cell voltageclamp configuration (V_(hold)=−40 mV).

FIG. 9B is a graph showing the concentration-response curve forcapsaicin (squares) and resiniferatoxin (open circles) in VR1-expressingoocytes. In FIG. 9B, the membrane currents were normalized in eachoocyte to a response obtained with 1 μM capsaicin and expressed as apercent of maximal response to capsaicin. Each pont represents meanvalues (±s.e.m.) from 5 independent oocytes.

FIG. 10A is a graph showing the effects of capsazepine uponcapsaicin-induced current in whole cell voltage clamp experiments. Slashmarks represent wash out periods of 2 and 3 min, respectively (n=3).cap=capsaicin; cpz=capsazepine; RR=ruthenium red. Each point represents4 independent oocytes. Current response were normalized to that elicitedby capsaicin in each oocyte (0.6 μM, open diamond). Slash marks denote 2and 12 minute wash out periods, respectively (n=3).

FIG. 10B is a graph showing the capsazepine inhibition curve ofcapsaicin response in whole cell voltage clamp studies.

FIG. 11 is a histogram with corresponding current traces reflecting therelative capsaicin content of several different hot peppers.

FIG. 12 is a graph showing induction of cell death in HEK293 cellstransiently transfected with capsaicin receptor-encoding cDNA. Openbars=cells exposed to carrier alone (ethanol); filled bars=cells exposedto capsaicin; pcDNA3=control cells without capsaicin receptor-encodingDNA; VR1 (1:50)=cells transiently transfected with capsaicin receptor-sencoding cDNA diluted 1:50 with control pcDNA3; and VR1=cellstransiently transfected with capsaicin receptor-encoding cDNA alone.Asterisks indicate a significant difference from ethanol-treated cells.

FIG. 13 is a current trace showing the effect of hydrogen ions uponcapsaicin receptor activity in oocytes expressing capsaicin receptor.cap on=time of capsaicin introduction; cap off=time of capsaicin washout The pH of the bath solution was changed during the experiment asindicated by the horizontal bars.

FIG. 14 is a graph showing a summary of the current response obtainedfrom nine independent capsaicin receptor-expressing oocytes. The greyportion of each bar indicates peak current evoked by capsaicin at pH7.6, while the black portion represents the additional current evoked bychanging the bath solution to pH 6.3.

FIG. 15A is a current trace showing the effects of heat and capsaicinupon capsaicin receptor activity in capsaicin receptor-expressing HEK293cells as determined by whole patch clamp analysis. FIG. 15B is a graphshowing the current-voltage relationship of the data obtained in FIG.15A.

FIG. 16 is a graph showing activation of capsaicin receptor in capsaicinreceptor-expressing Xenopus oocytes by noxious, but not innocuous, heat.The asterisk indicates a significant difference from controlwater-injected oocytes.

FIG. 17 provides representative current traces of the effect ofcapsaicin, heat, and heat plus ruthenium red (RR) upon capsaicinreceptor-expressing Xenopus oocytes and control water-injected oocytes.

FIG. 18 is a schematic illustrating the relationship between rat VR1,rat VRRP-1, and the human EST sequence AA321554.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

“Polynucleotide” as used herein refers to an oligonucleotide,nucleotide, and fragments or portions thereof, as well as to peptidenucleic acids (PNA), fragments, portions or antisense molecules thereof,and to DNA or RNA of genomic or synthetic origin which can be single- ordouble-stranded, and represent the sense or antisense strand. Where“polynucleotide” is used to refer to a specific polynucleotide sequence(e.g. a capsaicin receptor-encoding polynucleotide or a capsaicinreceptor-related polypeptide-encoding polynucleotide), “polynucleotide”is meant to encompass polynucleotides that encode a polypeptide that isfunctionally equivalent to the recited polypeptide, e.g.,polynucleotides that are degenerate variants, or polynucleotides thatencode biologically active variants or fragments of the recitedpolypeptide. Similarly, “polypeptide” as used herein refers to anoligopeptide, peptide, or protein. Where “polypeptide” is recited hereinto refer to an amino acid sequence of a naturally-occurring proteinmolecule, “polypeptide” and like terms are not meant to limit the aminoadd sequence to the complete, native amino acid sequence associated withthe recited protein molecule.

By “antisense polynucleotide” is mean a polynucleotide having anucleotide sequence complementary to a given polynucleotide sequence(e.g, a polynucleotide sequence encoding a capsaicin receptor) includingpolynucleotide sequences associated with the transcription ortranslation of the given polynucleotide sequence (e.g, a promoter of apolynucleotide encoding capsaicin receptor), where the antisensepolynucleotide is capable of hybridizing to a capsaicin receptorpolynucleotide sequence. Of particular interest are antisensepolynucleotides capable of inhibiting transcription and/or translationof a capsaicin receptor-encoding or capsaicin receptor-relatedpolypeptide-encoding polynucleotide either in vitro or in vivo.

“Peptide nucleic acid” as used herein refers to a molecule whichcomprises an oligomer to which an amino acid residue, such as lysine,and an amino group have been added. These small molecules, alsodesignated anti-lene agents, stop transcript elongation by binding totheir complementary (template) strand of nucleic acid (Nielsen et al1993 Anticancer Drug Des 8:53–63).

As used herein, “capsaicin receptor” or “capsaicin receptor polypeptide”means a recombinant or nonrecombinant polypeptide having an amino acidsequence of i) a native capsaicin receptor polypeptide, ii) abiologically active fragment of a capsaicin receptor polypeptide, iii)biologically active polypeptide analogs of a capsaicin receptorpolypeptide, or iv) a biologically active variant of a capsaicinreceptor polypeptide. Capsaicin receptor polypeptides of the inventioncan be obtained from any species, particularly mammalian, includinghuman, rodentia (e.g., murine or rat), bovine, ovine, porcine, murine,or equine, preferably rat or human, from any source whether natural,synthetic, semi-synthetic or recombinant. The term “capsaicin receptor”as used herein encompasses the vanilloid receptor subtype 1 (VR1)described in detail herein, but is not meant to be limited to VR1, andparticularly may be generically used to refer to the receptor subtypesVR1 and VR2.

As used herein, “capsaicin receptor-related polypeptide” or“vanilloid-like receptor (VLR) polypeptide” means a recombinant ornonrecombinant polypeptide having an amino acid sequence of i) a nativecapsaicin receptor-related polypeptide, ii) a biologically activefragment of a capsaicin receptor-related polypeptide, iii) biologicallyactive polypeptide analogs of a capsaicin receptor-related polypeptide,or iv) a biologically active variant of a capsaicin receptor-relatedpolypeptide, herein referred to as “VRRP-1”, “VLR1,” or “VR2”. Capsaicinreceptor polypeptides of the invention can be obtained from any species,particularly a mammalian species, including human, rodentia (e.g.,murine or rat), bovine, ovine, porcine, murine, or equine, preferablyrat or human, from any source whether natural, synthetic, semi-syntheticor recombinant. The term “capsaicin receptor-related polypeptide” asused herein also encompasses any polypeptide having at least about 40%identity, preferably at least about 45% identity, more preferably atleast about 49% identity to an amino acid sequence of a capsaicinreceptor polypeptide of the same species (e.g., rat or human capsaicinreceptor polypeptide). The term “capsaicin receptor-relatedpolypeptide-encoding sequence” also encompasses a nucleotide sequencehaving at least about 50% identity, preferably at least about 55%identity, more preferably at least about 59% identity to a nucleotidesequence of a capsaicin receptor polypeptide of the same species. In oneembodiment, the capsaicin receptor-related polypeptide interacts withcapsaicin receptor. “Capsaicin receptor-related polypeptide” as usedherein encompasses the vanilloid receptor-related polypeptide 1 (VRRP-1)described in detail herein, but is not meant to be limited to VRRP-1.

As used herein, “antigenic amino acid sequence” means an amino acidsequence that, either alone or in association with a carrier molecule,can elicit an antibody response in a mammal.

A “variant” of a capsaicin receptor or capsaicin receptor-relatedpolypeptide is defined as an amino acid sequence that is altered by oneor more amino acids. The variant can have “conservative” changes,wherein a substituted amino acid has similar structural or chemicalproperties, e.g., replacement of leucine with isoleucine. More rarely, avariant can have “nonconservative” changes, e.g., replacement of aglycine with a tryptophan. Similar minor variations can also includeamino acid deletions or insertions, or both. Guidance in determiningwhich and how many amino acid residues may be substituted, inserted ordeleted without abolishing biological or immunological activity can befound using computer programs well known in the art, for example,DNAStar software.

A “deletion” is defined as a change in either amino acid or nucleotidesequence in which one or more amino acid or nucleotide residues,respectively, are absent as compared to an amino acid sequence ornucleotide sequence of a naturally occurring capsaicin receptor orcapsaicin receptor-related polypeptide.

An “insertion” or “additon” is that change in an amino acid ornucleotide sequence which has resulted in the addition of one or moreamino acid or nucleotide residues, respectively, as compared to an aminoacid sequence or nucleotide sequence of a naturally occurring capsaicinreceptor or capsaicin receptor-related polypeptide.

A “substitution” results from the replacement of one or more amino acidsor nucleotides by different amino acids or nucleotides, respectively ascompared to an amino acid sequence or nucleotbde sequence of a naturallyoccurring capsaicin receptor or capsaicin receptor-related polypeptide.

The term “biologically active” refers to capsaicin receptor polypeptideor capsaicin receptor-related polypeptide having structural, regulatory,or biochemical functions of a naturally occurring capsaicin receptorpolypeptide or capsaicin receptor-related polypeptide, respectively.Likewise, “immunologically active” defines the capability of thenatural, recombinant or synthetic capsaicin receptor (or capsaicinreceptor-related polypeptide), or any oligopeptide thereof, to induce aspecific immune response in appropriate animals or cells and to bindwith specific antibodies.

The term “derivative” as used herein refers to the chemical modificationof a nucleic acid encoding a capsaicin receptor or a capsaicinreceptor-related polypeptide. Illustrative of such modifications wouldbe replacement of hydrogen by an alkyl, acyl, or amino group. A nucleicacid derivative would encode a polypeptide which retains essentialbiological characteristics of a natural capsaicin receptor or capsaicinreceptor-related polypeptide.

As used herein the term “isolated” is meant to describe a compound ofinterest (e.g., either a polynucleotide or a polypeptide) that is in anenvironment different from that in which the compound naturally occurs.“Isolated” is meant to include compounds that are within samples thatare substantially enriched for the compound of interest and/or in whichthe compound of interest is partially or substantially purified.

As used herein, the term “substantially purified” refers to a compound(e.g., either a polynucleotide or a polypeptide) that is removed fromits natural environment and is at least 60% free, preferably 75% free,and most preferably 90% free from other components with which it isnaturally associated.

“Stringency” typically occurs in a range from about Tm-5° C. (5° C.below the Tm of the probe) to about 20° C. to 25° C. below Tm. As willbe understood by those of skill in the art, a stringency hybridizationcan be used to identify or detect identical polynucleotide sequences orto identify or detect similar or related polynucleotide sequences.

The term “hybridization” as used herein shall include “any process bywhich a strand of nucleic acid joins with a complementary strand throughbase pairing” (Coombs 1994 Dictionary of Biotechnology, Stockton Press,New York N.Y.). Amplification as carried out in the polymerase chainreaction technologies is described in Dieffenbach et al. 1995, PCRPrimer, a Laboratory Manual, Cold Spring Harbor Press, Plainview N.Y.

“Sequence identity” as used herein generally refers to a sequenceidentity of nucleotide or amino acid sequence, where the sequenceidentity is generally at least about 65%, preferably at least about 75%,more preferably at least about 85%, and can be greater than at leastabout 90% or more as determined by the Smith-Waterman homology searchalgorithm as implemented in MPSRCH program (Oxford Molecular). For thepurposes of this invention, a preferred method of calculating percentidentity is the Smith-Waterman algorithm, using the following. GlobalDNA sequence identity must be greater than 65% as determined by theSmith-Waterman homology search algorithm as implemented in MPSRCHprogram (Oxford Molecular) using an affine gap search with the followingsearch parameters: gap open penalty, 12; and gap extension penalty, 1.

The term “transgene” is used herein to describe genetic material whichhas been or is about to be artificially inserted into the genome of amammalian, particularly a mammalian cell of a living animal.

By “transgenic animal” is meant a non-human animal, usually a mammal,having a non-endogenous (i.e., heterologous) nucleic acid sequencepresent as an extrachromosomal element in a portion of its cells orstably integrated into its germ line DNA (i.e., in the genomic sequenceof most or all of its cells). Heterologous nucleic acid is introducedinto the germ line of such transgenic animals by genetic manipulationof, for example, embryos or embryonic stem cells of the host animal.

A “knock-out of a target gene means an alteration in the sequence of thegene that results in a decrease of function of the target gene,preferably such that target gene expression is undetectable orinsignificant. For example, a knock-out of a capsaicin receptor genemeans that function of the capsaicin receptor has been substantiallydecreased so that capsaicin receptor expression is not detectable oronly present at insignificant levels. “Knock-out” transgenics of theinvention can be transgenic animals having a heterozygous or homozygousknock-out of the capsaicin receptor gene or capsaicinreceptor-related-polypeptide encoding sequence. “Knock-outs” alsoinclude conditional knock-outs, where alteration of the target gene canoccur upon, for example, exposure of the animal to a substance thatpromotes target gene alteration, introduction of an enzyme that promotesrecombination at the target gene site (e.g., Cre in the Cre-lox system),or other method for directing the target gene alteration postnatally.

A “knock-in” of a target gene means an alteration in a host cell genomethat results in altered expression (e.g., increased (including ectopic)or decreased expression) of the target gene, e.g., by introduction of anadditional copy of the target gene, or by operatively inserting aregulatory sequence that provides for enhanced expression of anendogenous copy of the target gene. For example, “knock-in” transgenicsof the invention can be transgenic animals having a heterozygous orhomozygous knock-in of the capsaicin receptor gene. “Knock-ins”, alsoencompass conditional knock-ins.

The major genetic sequences provided herein are as follows:

SEQ ID NO Sequence 1 Rat VR1 cDNA sequence 2 Rat VR1 amino acid sequence3 Rat VRRP-1 (VR2) cDNA sequence 4 Rat VRRP-1 (VR2) amino acid sequence5 Human VRRP-1 consensus sequence, region A 6 Human VRRP-1 consensussequence, region B 7 Human VRRP-1 consensus sequence, region C 8 ESTAA321554 DNA sequence 9 EST AA321554 amino acid sequence 10 mouse VR1cDNA sequence 11 mouse VR1 amino acid sequence 12 primer 13 primer 14Rat VR1 amino acid sequence 15 Human T11251 amino acid sequence 16Caliphora z80230 amino acid sequence 17 Drosophila TRP amino acidsequence 18 Bocine x99792 amino acid sequence 19 E. elegans z72508 aminoacid sequence 20 Human VRRP-1 (VR2) DNA sequence 21 Human VRRP-1 (VR2)DNA sequence 22 Human VRRP-1 (VR2) DNA sequence 23 Human VRRP-1 (VR2)amino acid sequence 24 Chicken VR1 cDNA sequence 25 Chicken VR1 aminoacid sequence 26 Human VR1 cDNA sequence 27 Human VR1 amino acidsequence 33 Human VR1 cDNA sequence 34 Human VR1 amino acid sequence 35Human VR2 cDNA sequence 36 Human VR2 amino acid sequenceOverview of the Invention

The present invention is based upon the identification and isolation ofa polynucleotide sequence encoding a capsaicin receptor polypeptide(e.g., the vanilloid receptor subtype 1 (VR1) polypeptide describedherein) and a capsaicin receptor-related polypeptide (e.g., thevanilloid receptor-related polypeptide 1 (VRRP-1; or VR2) describedherein). The corresponding genetic sequences are provided in theSeqlist, and are listed in the table provided above. Accordingly, thepresent invention encompasses such polynucleotides encoding capsaicinreceptor and/or capsaicin receptor-related polypeptides, as well as thecapsaicin receptor and capsaicin receptor-related polypeptides encodedby such polynucleotides.

A capsaicin receptor polypeptide-encoding polynucleotide was firstisolated by virtue of the capsaicin receptor polypeptide-encodingsequence to facilitate expression of a functional capsaicin receptor ina cellular assay. In short, the capsaicin receptor polypeptide-encodingpolynucleotide, when expressed in a mammalian or amphibian host cell,facilitated an increase in intracellular calcium concentration in thehost cell upon exposure to the agonist capsaicin. This work lead toidentification and isolation of a polynucleotide sequence encoding acapsaicin receptor referred to herein as a vanilloid receptor subtype 1(VR1). The capsaicin receptor-encoding VR1 sequence was then used toisolate by PCR amplification a sequences encoding related polypeptides,resulting in isolation and identification of sequences encoding acapsaicin receptor-related polypeptide, of which VRRP-1 (VR2) isexemplary.

The invention also encompasses use of capsaicin receptor and capsaicinreceptor-related polypeptide nucleic acid and amino acid sequences inthe identification of capsaicin receptor-binding compounds, particularlycapsaicin receptor-binding compounds having capsaicin receptor agonistor antagonist activity. The invention further encompasses the use of thepolynucleotides disclosed herein to facilitate identification andisolation of polynucleotide and polypeptide sequences having homology toa capsaicin receptor and/or capsaicin receptor-related polypeptide ofthe invention; as well as the diagnosis, prevention and treatment ofdisease and/or pain syndromes associated with capsaicin receptorbiological activity.

The polynucleotides of the invention can also be used as a molecularprobe with which to determine the structure, location, and expression ofcapsaicin receptor, receptor subtypes, and capsaicin receptor-relatedpolypeptides in mammals (including humans) and to investigate potentialassociations between disease states or clinical disorders (particularlythose involving acute and chronic pain or inflammation) and defects oralterations in receptor structure, expression, or function.

Capsaicin Receptor and Capsaicin Receptor-Related Polypeptide CodingSequences

In accordance with the invention, any nucleic acid sequence that encodesan amino acid sequence of a capsaicin receptor polypeptide or capsaicinreceptor-related polypeptide can be used to generate recombinantmolecules which express a capsaicin receptor polypeptide or capsaicinreceptor-related polypeptide, respectively. The nucleic acidcompositions used in the subject invention may encode all or a part of acapsaicin receptor polypeptide or capsaicin receptor-related polypeptideof the invention as appropriate. Fragments may be obtained of the DNAsequence by chemically synthesizing oligonucleotides in accordance withconventional methods, by restriction enzyme digestion, by PCRamplification, etc. For the most part, DNA fragments will be of at leastabout ten contiguous nucleotides, usually a least about 15 nt, moreusually at least about 18 nt to about 20 nt, more usually at least about25 nt to about 50 nt. Such small DNA fragments are useful as primers forPCR, hybridization screening, etc. Larger DNA fragments, i.e. greaterthan 100 nt are useful for production of the encoded polypeptide.

The nucleic acid and deduced amino acid sequences of rat capsaicinreceptor (subtype VR1) are provided as SEQ ID NOS:1 and 2. Nucleic acidand deduced amino acid sequences of a human capsaicin receptor (subtypeVR1) are provided as SEQ ID NOS:33 and 34. A nucleotide sequenceencoding murine capsaicin receptor subtype VR1 comprises the sequencesof SEQ ID NOS:10 and 11. The chicken capsaicin receptor subtype VR1 isprovided as SEQ ID NO:24 and 25.

The nucleic acid and deduced amino acid sequence of rat capsaicinreceptor-related polypeptide 1 (VRRP-1; or subtype VR2) are provided asSEQ ID NO:3 and 4, respectively. A sequence encoding a human capsaicinreceptor-related polypeptide (referred to as human VR2) comprises thenucleotide sequence SEQ ID NOS:35 and 36.

The present invention also encompasses variants of capsaicin receptorand capsaicin receptor-related polypeptides. A preferred variant is onehaving at least 80% amino acid sequence similarity, more preferably atleast 90% amino acid sequence similarity, still more preferably at least95% amino acid sequence similarity to an amino acid sequence of acapsaicin receptor, subtype VR1 or VR2.

It will be appreciated by those skilled in the art that as a result ofthe degeneracy of the genetic code, a multitude of degenerate variantsof nucleotide sequences encoding capsaicin receptor and capsaicinreceptor-related polypeptides, some bearing minimal homology to thenucleotide sequences of any known and naturally occurring gene, can beproduced. The invention contemplates each and every possible variationof nucleotide sequence that can be made by selecting combinations basedon possible codon choices. These combinations are made in accordancewith the standard triplet genetic code as applied to the nucleotidesequence of naturally occurring capsaicin receptor or capsaicinreceptor-related polypeptide, and all such variations are to beconsidered as being specifically disclosed herein.

Although nucleotide sequences that encode capsaicin receptorpolypeptides, and their variants are preferably capable of hybridizingto the nucleotide sequence of the naturally occurring polypeptides underappropriately selected conditions of stringency, it may be advantageousto produce nucleotide sequences encoding receptors or their derivativespossessing a substantially different codon usage. Codons can be selectedto increase the rate at which expression of the polypeptide occurs in aparticular prokaryotic or eukaryotic expression host in accordance withthe frequency with which particular codons are utilized by the host.Other reasons for substantially altering the nucleotide sequenceencoding capsaicin receptor, capsaicin receptor-related polypeptide, andtheir derivatives without altering the encoded amino acid sequencesinclude the production of RNA transcripts having more desirableproperties (e.g., increased half-life) than transcripts produced fromthe naturally occurring sequence.

Nucleotide sequences encoding a capsaicin receptor polypeptide,capsaicin receptor-related polypeptide, and/or their derivatives can besynthesized entirely by synthetic chemistry, after which the syntheticgene can be inserted into any of the many available DNA vectors andexpression systems using reagents that are well known in the art at thetime of the filing of this application. Moreover, synthetic chemistrycan be used to introduce mutations into a sequence encoding a capsaicinreceptor polypeptide or capsaicin receptor-related polypeptide.

Also included within the scope of the present invention arepolynucleotide sequences that are capable of hybridizing to thenucleotide sequence of any of the provided nucleic acid sequences ofcapsaicin receptors, subtypes VR1 or VR2. Of particular interest arepolynucleotide sequence capable of hybridizing under various conditionsof stringency to the coding sequence for capsaicin receptor or capsaicinreceptor-related polypeptide (e.g., nucleotides 81–2594 of SEQ ID NO:1,or nucleotides 14–2530 of SEQ ID NO:33), to a region of a capsaicinreceptor-encoding sequence or capsaicin receptor-relatedpolypeptide-encoding sequence that shares homology with other suchsequences (e.g., a sequence encoding a contiguous stretch of amino acidresidues present in SEQ ID NO:2 (e.g., amino acid residues 636 to 706 ofSEQ ID NO:2), a sequence encoding a contiguous streatch of amino acidresidues present in SEQ ID NO:33 (e.g., amino add residues 636 to 706 ofSEQ ID NO:33), and other sequences representing areas of homology withother capsaicin receptor-encoding sequences and/or capsaicinreceptor-related polypeptides-encoding sequences, as well as sequencesthat uniquely identify capsaicin receptor-encoding sequences orcapsaicin receptor-related polypeptide-encoding sequences of variousspecies. Of particular interest are capsaicin receptor VR1 or VR2polynucleotide sequences encoding a human capsaicin receptor polypeptideor human capsaicin receptor-related polypeptide. Hybridizationconditions are based on the melting temperature (Tm) of the nucleic acidbinding complex or probe, as taught in Berger et al. 1987 Guide toMolecular Cloning Techniques, Methods in Enzymology, Vol 152, AcademicPress, San Diego Calif. incorporated herein by reference, and can beused at a defined stringency.

Altered nucleic acid sequences encoding capsaicin receptor or capsaicinreceptor-related polypeptide that can be used in accordance with theinvention include deletions, insertions or substitutions of differentnucleotides resulting in a polynucleotide that encodes the same or afunctionally equivalent capsaicin receptor or capsaicin receptor-relatedpolypeptide. The protein can also comprise deletions, insertions orsubstitutions of amino add residues that result in a polypeptide that isfunctionally equivalent to capsaicin receptor or capsaicinreceptor-related polypeptide. Deliberate amino acid substitutions can bemade on the basis of similarity in polarity, charge, solubility,hydrophobicity, hydrophilicity, and/or the amphipathic nature of theresidues with the proviso that biological activity of capsaicin receptoris retained. For example, negatively charged amino acids includeaspartic add and glutamic acid; positively charged amino acids includelysine and arginine; and amino acids with uncharged polar head groupshaving similar hydrophilicity values include leucine, isoleucine,valine; glycine, alanine; asparagine, glutamine; serine, threoninephenylalanine, and tyrosine.

Alleles of capsaicin receptor, as well as alleles of capsaicinreceptor-related polypeptide, are also encompassed by the presentinvention. As used herein, an “allele” or “allelic sequence” is analternative form of a capsaicin receptor or capsaicin receptor-relatedpolypeptide. Alleles result from a mutation (i.e., an alteration in thenucleic acid sequence) and generally produce altered mRNAs and/orpolypeptides that may or may not have an altered structure or functionrelative to naturally-occurring capsaicin receptor or capsaicinreceptor-related polypeptide. Any given gene may have none, one, or manyallelic forms. Common mutational changes that give rise to alleles aregenerally ascribed to natural deletions, additions or substitutions ofamino acids. Each of these types of changes may occur alone or incombination with the other changes, and may occur once or multiple timesin a given sequence.

Isolating Capsaicin Receptor-Encoding and Capsaicin Receptor-RelatedPolypeptide-Encoding Polynucleotides from Other Species

Capsaicin receptor polypeptide-encoding polynucleotides, capsaicinreceptor-related polypeptide-encoding polynucleotides, or portionsthereof can be used as probes for identifying and cloning homologs ofthe capsaicin receptor and capsaicin receptor-related polypeptidesequences disclosed herein. Of particular interest are mammalianhomologs (especially the human homology of the disclosed rat capsaicinreceptor-encoding and capsaicin receptor-related polypeptide-encodingsequences), where the homologs have substantial sequence similarity toone another, i.e. at least 40%, usually at least 60%, more usually atleast 75%, usually at least 90%, more usually at least 95% sequencesimilarity. Mammalian homologs of capsaicin receptor may also share ahigh degree of similarity to the capsaicin receptor disclosed herein inthe vicinity of the predicted pore-loop and sixth transmembrane domains.At these regions the capsaicin receptor homologs may exhibit highsequence similarity, e.g., at least about 40% amino acid sequenceidentity, usually at least about 60% to 75% amino acid sequenceidentity, with at least about 40% nucleotide sequence similarity,usually at least about 60% to 90% nucleotide sequence similarity.

Sequence similarity is calculated based on a reference sequence, whichmay be a subset of a larger sequence, such as a conserved motif, codingregion, flanking region, etc. A reference sequence will usually be atleast about 18 nt long, more usually at least about 30 nt long, and mayextend to the complete sequence that is being compared. Algorithms forsequence analysis are known in the art, such as BLAST, described inAltschul et al. (1990) J Mol Biol 215:403–10. The specificity of theprobe, whether it is made from a highly specific region, e.g., 10 uniquenucleotides in the 5′ regulatory region, or a less specific region,e.g., especially in the 3′ region, and the stringency of thehybridization or amplification (maximal, high, intermediate or low) willdetermine whether the probe identifies only naturally occurringsequences encoding capsaicin receptor, alleles or related sequences.

Where the probes of the invention are used in the detection of relatedsequences, the probes preferably comprise at least 30%, more preferablyat least 50% of the nucleotides from any of the capsaicin receptorpolypeptide-encoding sequences or the capsaicin receptor-relatedpolypeptide-encoding described herein. The hybridization probes of thesubject invention can be derived from the provided VR1 and VR2nucleotide sequences, or from their corresponding genomic sequencesincluding promoters, enhancer elements and introns of the naturallyoccurring capsaicin receptor-encoding sequence. Hybridization probes canbe detectably labeled with a variety of reporter molecules, includingradionuclides (e.g., ³²P or ³⁵S), or enzymatic labels (e.g., alkalinephosphatase coupled to the probe via avidin/biobn coupling systems), andthe like.

Specific hybridization probes can also be produced by cloning theprovided nucleic acid sequences into vectors for production of mRNAprobes. Such vectors, which are known in the art and are commerciallyavailable, can be used to synthesize RNA probes in vitro using anappropriate RNA polymerase (e.g, T7 or SP6 RNA polymerase) andappropriate radioactively labeled nucleotides.

Nucleic acids having sequence similarity are detected by hybridizationunder low stringency conditions, for example, at 50° C. and 10×SSC (0.9M saline/0.09 M sodium citrate) and remain bound when subjected towashing at 55° C. in 1×SSC. Sequence identity may be determined byhybridization under stringent conditions, for example, at. 50° C. orhigher and 0.1×SSC (9 mM saline/0.9 mM sodium citrate). By using probes,particularly labeled probes of DNA sequences, one can isolate homologousor related genes. The source of homologous genes may be any species,e.g. primate species, particularly human; rodents, such as rats andmice, canines, felines, bovines, ovines, equines, yeast, Drosophila,Caenhorabditis, etc. Of particular interest is the identification andisolation of human capsaicin receptor polypeptide-encodingpolynucleotides and human capsaicin receptor-relatedpolypeptide-encoding polynucleotides.

The capsaicin receptor and capsaicin receptor-related polypeptidenucleic acid sequences can also be used to generate hybridization probesfor mapping a naturally occurring genomic sequence. The sequence can bemapped to a particular chromosome or to a specific region of thechromosome using well known techniques. These include in situhybridization to chromosomal spreads, flow-sorted chromosomalpreparations, or artificial chromosome constructions such as yeastartificial chromosomes, bacterial artificial chromosomes, bacterial P1constructions or single chromosome cDNA libraries as reviewed in Price1993; Blood Rev 7:127–34 and Trask 1991; Trends Genet 7:149–54.Fluorescent in situ hybridization of chromosome spreads is described in,for example, Verma et al 1988 Human Chromosomes: A Manual of BasicTechniques, Pergamon Press, New York N.Y.

Information from chromosomal mapping of sequences encoding capsaicinreceptor or capsaicin receptor-related polypeptide can be correlatedwith additional genetic map data. Correlation between the location of acapsaicin receptor-encoding sequence, or a capsaicin receptor-relatedpolypeptide-encoding sequence, on a physical chromosomal map and aspecific disease (or predisposition to a specific disease) can helpdelimit the region of DNA A associated with that genetic disease. Thenucleotide sequences of the subject invention can be used to detectdifferences in gene sequences (e.g., differences in the chromosomallocation due to translocation, inversion, etc. or other differences inthe capsaicin receptor-encoding region due to insertional mutation(s) ordeletion of capsaicin receptor- or capsaicin receptor-relatedpolypeptide-encoding sequences) between normal, carrier, or affectedindividuals. Exemplary disorders that may benefit from such informationinclude, but are not necessarily limited to, complex regional painsyndromes, reflex sympathetic dystrophies, postherpetic neuralgia,psoriasis, reactive airway diseases (e.g., asthma, chronic obstructivepulmonary disease), osteoarthritis, rheumatoid arthritis, diabeticneuropathy, AIDS-associated neuropathies, and hereditary neuropathies(e.g, associated with capsaicin receptor dysfunction).

Extending the Capsaicin Receptor-Encoding Polynucleotide Sequence

The polynucleotide sequence encoding capsaicin receptor or capsaicinreceptor-related polypeptide can be extended utilizing partialnucleotide sequence and various methods known in the art to detectupstream sequences such as promoters and regulatory elements. Gobinda etal 1993; PCR Methods Applic 2:318–22 disclose restriction-site”polymerase chain reaction (PCR) as a direct method which uses universalprimers to retrieve unknown sequence adjacent to a known locus. First,genomic DNA is amplified in the presence of primer to a linker sequenceand a primer specific to the known region. The amplified sequences aresubjected to a second round of PCR with the same linker primer andanother specific primer internal to the first one. Products of eachround of PCR are transcribed with an appropriate RNA polymerase andsequenced using reverse transcriptase.

Inverse PCR can be used to amplify or extend sequences using divergentprimers based on a known region (Triglia et al 1988 Nucleic Acids Res16:8186). The primers can be designed using OLIGO® 4.06 Primer AnalysisSoftware (1992; National Biosciences Inc, Plymouth Minn.), or anotherappropriate program, to be 22–30 nucleotides in length, to have a GCcontent of 50% or more, and to anneal to the target sequence attemperatures about 68°–72° C. This method uses several restrictionenzymes to generate a suitable fragment in the known region of a gene.The fragment is then circularized by intramolecular ligation and used asa PCR template.

Capture PCR (Lagerstrom et al 1991 PCR Methods Applic 1:111–19) is amethod for PCR amplification of DNA fragments adjacent to a knownsequence in human and yeast artificial chromosome DNA Capture PCR alsorequires multiple restriction enzyme digestions and ligations to placean engineered double-stranded sequence into an unknown portion of theDNA molecule before PCR.

Another method that can be used to retrieve unknown sequences is that ofParker et al 1991; Nucleic Acids Res 19:3055–60. Additionally, one canuse PCR, nested primers, and PromoterFinder libraries to “Walk in”genomic DNA (PromoterFinder™ Clontech (Palo Alto Calif.). This processavoids the need to screen libraries and is useful in finding intron/exonjunctions. Preferably, the libraries used to identify full length cDNAshave been size-selected to include larger cDNAs. More preferably, thecDNA libraries used to identify full-length cDNAs are those generatedusing random primers, in that such libraries will contain more sequencescomprising regions 5′ of the sequence(s) of interest. A randomly primedlibrary can be particularly useful where oligo d(T) libraries do notyield a full-length cDNA. Genomic libraries are preferred foridentification and isolation of 5′ nontranslated regulatory regions of asequence(s) of interest.

Capillary electrophoresis can be used to analyze the size of, or confirmthe nucleotide sequence of, sequencing or PCR products. Systems forrapid sequencing are available from Perkin Elmer, Beckman Instruments(Fullerton Calif.), and other companies. Capillary sequencing can employflowable polymers for electrophoretic separation, four different,laser-activatable fluorescent dyes (one for each nucleotide), and acharge coupled device camera for detection of the wavelengths emitted bythe fluorescent dyes. Output/light intensity is converted to electricalsignal using appropriate software (e.g. Genotyper™ and SequenceNavigator™ from Perkin Elmer). The entire process from loading of thesamples to computer analysis and electronic data display is computercontrolled. Capillary electrophoresis is particularly suited to thesequencing of small pieces of DNA that might be present in limitedamounts in a particular sample. Capillary electrophoresis providesreproducible sequencing of up to 350 bp of M13 phage DNA in 30 min(Ruiz-Martinez et al 1993 Anal Chem 65:2851–2858).

Production of Polynucleotides Encoding Capsaicin Receptor or CapsaicinReceptor-Related Polypeptides

In accordance with the present invention, polynucleotide sequences thatencode capsaicin receptor polypeptides or capsaicin receptor-relatedpolypeptides (which capsaicin receptor polypeptides and capsaicinreceptor-related polypeptides include fragments of thenaturally-occurring polypeptide, fusion proteins, and functionalequivalents thereof) can be used in recombinant DNA molecules thatdirect the expression of capsaicin receptor or capsaicinreceptor-related polypeptides in appropriate host cells. Due to theinherent degeneracy of the genetic code, other DNA sequences that encodesubstantially the same or a functionally equivalent amino acid sequence,can be used to clone and express capsaicin receptor or capsaicinreceptor-related polypeptide. As will be understood by those of skill inthe art, it may be advantageous to produce capsaicin receptor-encodingnucleotide sequences and capsaicin receptor-related polypeptide-encodingnucleotide sequences possessing non-naturally occurring codons. Codonspreferred by a particular prokaryotic or eukaryotic host (Murray et al1989 Nuc Acids Res 17:477–508) can be selected, for example, to increasethe rate of expression or to produce recombinant RNA transcripts havinga desirable characteristic(s) (e.g., longer half-life than transcriptsproduced from naturally occurring sequence).

The nucleotide sequences of the present invention can be engineered inorder to alter an capsaicin receptor-encoding sequence or a capsaicinreceptor-related polypeptide-encoding sequence for a variety of reasons,including but not limited to, alterations that facilitate the cloning,processing and/or expression of the gene product. For example, mutationscan be introduced using techniques that are well known in the art, e.g.,site-directed mutagenesis to insert new restriction sites, alterglycosylation patterns, change codon preference, produce splicevariants, etc.

In another embodiment of the invention, a natural, modified, orrecombinant polynucleotide encoding a capsaicin receptor polypeptide orcapsaicin receptor-related polypeptide can be ligated to a heterologoussequence to encode a fusion protein. Such fusion proteins can also beengineered to contain a cleavage site located between a capsaicinreceptor polypeptide-encoding sequence (or capsaicin receptor-relatedpolypeptide-encoding sequence) and a heterologous polypeptide sequence,such that the heterologous polypeptide sequence can be cleaved andpurified away from the capsaicin receptor polypeptide or capsaicinreceptor-related polypeptide.

In an alternative embodiment of the invention, a nucleotide sequenceencoding a capsaicin receptor polypeptide or capsaicin receptor-relatedpolypeptide can be synthesized, in whole or in part, using chemicalmethods well known in the art (see, e.g., Caruthers et al 1980 Nuc AcidsRes Symp Ser 215–23, Horn et al (1980) Nuc Acids Res Symp Ser 225–32).Alternatively, the polypeptide itself can be produced using chemicalmethods to synthesize an amino acid sequence of a capsaicin receptor orcapsaicin receptor-related polypeptide, in whole or in part. Forexample, peptide synthesis can be performed using various solid-phasetechniques (Roberge et al 1995 Science 269:202–204) and automatedsynthesis can be achieved, for example, using the ABI 431A PeptideSynthesizer (Perkin Elmer) in accordance with the instructions providedby the manufacturer.

The newly synthesized polypeptide can be substantially purified bypreparative high performance liquid chromatography (e.g., Creighton 1983Proteins, Structures and Molecular Principles, WH Freeman and Co, NewYork N.Y.). The composition of the synthetic polypeptides can beconfirmed by amino acid analysis or sequencing (e.g., the Edmandegradation procedure; Creighton, supra). Additionally the amino acidsequence of capsaicin receptor, capsaicin receptor-related polypeptide,or any part thereof, can be altered during direct synthesis and/orcombined using chemical methods with sequences from other proteins, orany part thereof, to produce a variant polypeptide.

Capsaicin Receptor and Capsaicin Receptor-Related Polypeptide ExpressionSystems

The invention encompasses expression of capsaicin receptor polypeptidesand capsaicin receptor-related polypeptides individually or incombination (e.g., co-expression). In order to express a biologicallyactive capsaicin receptor polypeptide and/or capsaicin receptor-relatedpolypeptide, the nucleotide sequence encoding a capsaicin receptorpolypeptide, a capsaicin receptor-related polypeptide, and/or afunctional equivalent of either, is inserted into an appropriateexpression vector, i.e., a vector having the necessary elements for thetranscription and translation of the inserted coding sequence. Methodswell known to those skilled in the art can be used to constructexpression vectors comprising a desired polypeptide-encoding sequenceand appropriate transcriptional or transitional controls. These methodsinclude in vitro recombinant DNA techniques, synthetic techniques and invivo recombination or genetic recombination. Such techniques aredescribed in Sambrook et al 1989. Molecular Cloning, A LaboratoryManual, Cold Spring Harbor Press, Plainview N.Y. and Ausubel et al 1989Current Protocols in Molecular Biology, John Wiley & Sons, New York N.Y.

A variety of expression vector/host cell systems can be utilized toexpress a capsaicin receptor polypeptide- and capsaicin receptor-relatedpolypeptide-encoding sequence. These include, but are not limited to,amphibian oocytes (e.g., Xenopus oocytes); microorganisms such asbacteria transformed with recombinant bacteriophage, plasmid or cosmidDNA expression vectors; yeast transformed with yeast expression vectors;insect cell systems infected with viral expression vectors (e.g.,baculovirus); plant cell systems transfected with viral expressionvectors (e.g., cauliflower mosaic virus, CaMV, tobacco mosaic virus,TMV) or transformed with bacterial expression vectors (e.g., Ti orpBR322 plasmid); or animal (e.g., mammalian) cell systems. Preferably,the sequences of the present invention, particularly capsaicinreceptor-encoding sequences, are expressed in a mammalian cell system(e.g., human embryonic kidney cells (e.g., HEK 293), an amphibian oocyte(e.g., by injecting Xenopus oocytes with complementary capsaicinreceptor-encoding RNA), or other host cell that is easily propagated inculture and can be transformed or transfected to either transiently orstably express, preferably stably express, a capsaicin receptor-encodingsequence and/or capsaicin receptor-related polypeptide-encodingsequence).

Host cells can be selected for capsaicin receptor polypeptide and/orcapsaicin receptor-related polypeptide expression according to theability of the cell to modulate the expression of the inserted sequencesor to process the expressed protein in a desired fashion. Suchmodifications of the polypeptide include, but are not limited to,acetylation, carboxylation, glycosylation, phosphorylation, lipidationand acylation. Post-translational processing that involves cleavage of a“prepro” form of the protein may also be important for correctpolypeptide folding, membrane insertion, and/or function. Host cellssuch as HEK 293, CHO, HeLa, MDCK, WI38, Xenopus oocytes, and others havespecific cellular machinery and characteristic mechanisms for suchpost-translational activities and may be chosen to ensure the correctmodification and processing of the introduced, foreign polypeptide.

The vector(s) used for expression of a capsaicin receptor polypeptideand/or capsaicin receptor-related polypeptide will vary with a varietyof factors including the host cell in which the capsaicin receptorpolypeptide is to be expressed, whether capsaicin receptor polypeptide-and capsaicin receptor-related polypeptide sequences are to beco-expressed either from a single construct or from separate constructs,and the intended use for the polypeptide produced. For example, whenlarge quantities of a capsaicin receptor polypeptide or capsaicinreceptor-related polypeptide are required (e.g., for the antibodyproduction), vectors that direct high-level expression of fusionproteins that can be readily purified may be desirable. Such vectorsinclude, for example, bacterial expression vectors, includingmultifunctional E. coli cloning and expression vectors such asBluescript® (Stratagene; which provides for production ofpolypeptide-β-galactosidase hybrid proteins); and pGEX vectors (Promega,Madison Wis.; which provides for production of glutathione S-transferase(GST) fusion proteins. Where the host cell is yeast (e.g., Saccharomycescerevisiae) a number of vectors containing constitutive or induciblepromoters such as alpha factor, alcohol oxidase and PGH can be used. Forreviews, see Ausubel et al (supra) and Grant et al 1987 Methods inEnzymology 153:516–544.

Where the host cell is a mammalian cells, a number of expression systemscan be used. For example, the expression vector can be derived from aviral-based expression system, such as an expression system derived froman adenovirus, SV40, CMV, or RSV nucleotide sequence. Expressionefficiency can be enhanced by including enhancers appropriate to thecell system in use (Scharf et al 1994 Results Probl Cell Differ20:125–62; Bittner et al 1987 Methods in Enzymol 153:516–544) (e.g., theRSV enhancer can be used to increase expression in mammalian hostcells).

The “control elements” or “regulatory sequences” of these systems, whichvary in their strength and specificities, are those nontranslatedregions of the vector, enhancers, promoters, and 3′ untranslated regionsthat interact with host cellular proteins to facilitate transcriptionand translation of a nucleotide sequence of interest. Depending on thevector system and host utilized, any number of suitable transcriptionaland translational elements, including constitutive and induciblepromoters, can be used. Such control elements or regulatory sequencesare selected according to the host cell in which the capsaicinreceptor-encoding polynucleotide and/or capsaicin receptor-relatedpolypeptide-encoding polynucleotide is to be expressed. For example, inmammalian cell systems, promoters from the mammalian genes or frommammalian viruses are most appropriate. Where it is desirable togenerate a cell line containing multiple copies of a capsaicin receptorpolypeptide-encoding sequence or a capsaicin receptor-relatedpolypeptide-encoding sequence, vectors derived from SV40 or EBV can beused in conjunction with other optional vector elements, e.g., anappropriate selectable marker.

Specific initiation signals may also be required for efficienttranslation of a capsaicin receptor polypeptide- or capsaicinreceptor-related polypeptide-encoding sequence, e.g., the ATG initiationcodon and flanking sequences for bacterial expression. Where a nativesequence, including its initiation codon and upstream sequences, isinserted into the appropriate expression vector, no additionaltranslational control signals may be needed. However, where only codingsequence, or a portion thereof, is inserted in an expression vector,exogenous transcriptional control signals including the ATG initiationcodon must be provided. Furthermore, the initiation codon must be in thecorrect reading frame to ensure transcription of the entire insertExogenous transcriptional elements and initiation codons can be derivedfrom various origins, and can be either natural or synthetic.

Where long-term, high-yield recombinant polypeptide production isdesired, stable expression is preferred. For example, cell lines thatstably express capsaicin receptor and/or capsaicin receptor-relatedpolypeptide can be transformed using expression vectors containing viralorigins of replication or endogenous expression elements and aselectable marker gene. After introduction of the vector, cells can begrown in an enriched media before they are exposed to selective media.The selectable marker, which confers resistance to the selective media,allows growth and recovery of cells that successfully express theintroduced sequences. Resistant, stably transformed cells can beproliferated using tissue culture techniques appropriate to the hostcell type.

Any number of selection systems can be used to recover transformed celllines. These include, but are not limited to, the herpes simplex virusthymidine kinase (Wigler et al 1977 Cell 11:223–32) and adeninephosphoribosyltransferase (Lowy et al 1980 Cell 22:817–23) genes whichcan be employed in tk- or aprt-cells, respectively. Also, antimetaboliteor antibiotic resistance can be used as the basis for selection; forexample, dhfr which confers resistance to methotrexate (Wigler et al1980 Proc Natl Acad Sci 77:3567–70); and npt, which confers resistanceto the aminoglycosides neomycin and G418 (Colbere-Garapin et al 1981 JMol Biol 150:1–14). Additional selectable genes have been described, forexample, trpB, which allows cells to utilize indole in place oftryptophan, or hisD, which allows cells to utilize histinol in place ofhistidine (Hartman et al. 1988 Proc Natl Acad Sci 85:8047–51).Selectable markers also include visible markers such as anthocyanins,β-glucuronidase and its substrate, GUS, and luciferase and itssubstrate, luciferin. Such visible markers are useful to both identifytransformants and to quantify the amount of transient or stable proteinexpression attributable to a specific vector system (Rhodes et al 1995Methods Mol Biol 55:121–131).

Alternatively, host cells that contain the coding sequence for andexpress capsaicin receptor polypeptides and/or capsaicinreceptor-related polypeptides can be identified by a variety ofprocedures known to those of skill in the art. These procedures include,but are not limited to, DNA-DNA or DNA-RNA hybridization and proteinbioassay or immunoassay techniques for the detection and/or quantitationof the nucleic acid or protein.

The presence of polynucleotide sequences encoding a capsaicin receptorand/or capsaicin receptor-related polypeptide can be detected by DNA-DNAor DNA-RNA hybridization or PCR amplification using probes, portions orfragments of polynucleotides encoding capsaicin receptor and/orcapsaicin receptor-related polypeptide. Nucleic add amplification-basedassays involve the use of oligonucleotides or oligomers based on asequence encoding a capsaicin receptor or capsaicin receptor-relatedpolypeptide to detect transformants containing the desired DNA or RNA.As used herein “oligonucleotides” or “oligomers” refer to a nucleic acidsequence of at least about 10 nucleotides and as many as about 60nucleotides, preferably about 15 to 30 nucleotides, and more preferablyabout 20–25 nucleotides which can be used as a probe or amplimer.

A variety of immunoassays for detecting and measuring the expression ofa specific protein, using either protein-specific polyclonal ormonoclonal antibodies are known in the art. Examples includeenzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA) andfluorescent activated cell sorting (FACS). These and other assays aredescribed in, e.g., Hampton et al 1990, Serological Methods, ALaboratory Manual, APS Press, St Paul Minn. and Maddox et al 1983, J ExpMed 158:1211.

A wide variety of detectable labels and conjugation techniques are knownthe art and can be used in various nucleic acid and amino acid assays.Means for producing labeled hybridization or PCR probes for detectingsequences related to sequences encoding a capsaicin receptor orcapsaicin receptor-related polypeptide include oligolabeling, nicktranslation, end-labeling or PCR amplification using a labelednucleotide. Alternatively, a nucleotide sequence encoding a capsaicinreceptor polypeptide or capsaicin receptor-related polypeptide can becloned into a vector for the production of an mRNA probe. Vectors andmethods for production of mRNA probes are well known in the art.Suitable reporter molecules or labels include those radionuclides,enzymes, fluorescent, chemiluminescent, or chromogenic agents as well assubstrates, cofactors, inhibitors, magnetic particles and the like, asdescribed in U.S. Pat. Nos. 3,817,837; 3,850,752; 3,939,350; 3,996,345;4,277,437; 4,275,149 and 4,366,241, each of which are incorporatedherein by reference.

In a preferred embodiment, host cells expressing capsaicin receptor arescreened and selected using a functional assay for capsaicin receptoractivity. For example, host cells expressing functional capsaicinreceptor can be screened for alterations in intracellular calciumconcentrations upon exposure to a capsaicin receptor binding compound(e.g., capsaicin or resiniferatoxin). Where the capsaicin receptorbinding compound is a capsaicin receptor agonist, binding of the agonistcompound to the capsaicin receptor result in increased levels ofintracellular calcium in the host cell expressing capsaicinreceptor-encoding nucleic acid. Methods and compositions (e.g., fura-2)for monitoring intracellular calcium concentration are well known in theart.

Purification of Capsaicin Receptor Polypeptides and CapsaicinReceptor-Related Polypeptides

Methods for production of a polypeptide after identification of itsencoding polynucleotide are well known in the art. Host cellstransformed with a nucleotide sequence(s) encoding a capsaicin receptorpolypeptide and/or capsaicin receptor-related polypeptide-can becultured under conditions suitable for the expression and recovery ofthe encoded polypeptide from cell culture. The polypeptide produced by arecombinant cell may be secreted or retained intracellularly dependingon the sequence and/or the vector used. As will be understood by thoseof skill in the art, expression vectors containing polynucleotidesencoding capsaicin receptor polypeptides or capsaicin receptor-relatedpolypeptides can be designed with signal sequences that direct secretionof the encoded polypeptide(s) through a prokaryotic or eukaryotic cellmembrane.

Purification of capsaicin receptor polypeptides and capsaicinreceptor-related polypeptides can be facilitated by using a recombinantconstruct that includes a nucleotide sequence(s) encoding one or morepolypeptide domains that, when expressed in-frame with the sequenceencoding the capsaicin receptor or capsaicin receptor-relatedpolypeptide, provides a fusion protein having apurification-facilitating domain (Kroll et al 1993 DNA Cell Biol12:441–53). A cleavable linker sequences(s) between the purificationdomain and the capsaicin receptor polypeptide- or capsaicinreceptor-related polypeptide-encoding sequence can be included tofurther facilitate purification.

Capsaicin receptor polypeptides and capsaicin receptor-relatedpolypeptides (each of which polypeptides encompass polypeptides having aportion of the native amino acid sequence) can also be produced bydirect peptide synthesis using solid-phase techniques (see, e.g.,Stewart et al 1969 Solid-Phase Peptide Synthesis, WH Freeman Co, SanFrancisco; Merrifield 1963 J Am Chem Soc 85:2149–2154). Variousfragments of capsaicin receptor or capsaicin receptor-relatedpolypeptide can be chemically synthesized separately and combined usingchemical methods to produce the full length molecule.

Methods for purifying a desired polypeptide following either artificialsynthesis or recombinant production are routine and well known in theart.

Uses of Capsaicin Receptor Polypeptides, Capsaicin Receptor-RelatedPolypeptides, and Nucleic Acid Encoding Capsaicin Receptor Polypeptidesor Capsaicin Receptor-Related Polypeptides

In addition to the uses described above, the nucleotide and polypeptidesequences disclosed herein can be used in a variety of ways, includingproduction of antibodies, identification of capsaicin receptor-bindingcompounds and capsaicin receptor-related polypeptide-binding compoundsthat affect capsaicin receptor function (e.g., in a drug screeningassay), and in the identification of other polynucleotide sequencesencoding capsaicin receptor polypeptides and capsaicin receptor-relatedpolypeptides. In addition, sequences encoding capsaicin receptorpolypeptides and capsaicin receptor-related polypeptides can be used indiagnostic assays (e.g., prenatal or postnatal diagnosis). Furthermore,capsaicin receptor-encoding sequences and their encoded polypeptides canalso be used in assays to assess the capsaicin content of a sample(e.g., from a natural product, e.g. a chili pepper extract) or thecapsaicin-promoting effects of an agent (e.g., a candidate agent for usea flavor enhancing additive to foods).

These and other applications of the sequences of the invention aredescribed in more detail below.

Screening for Capsaicin Receptor- and Capsaicin Receptor-RelatedPolypeptide Binding Compounds

Capsaicin receptor polypeptides and capsaicin receptor-relatedpolypeptides, each of which encompasses biologically active orimmunogenic fragments or oligopeptides thereof, can be used forscreening compounds that affect capsaicin receptor activity by, forexample, specifically binding capsaicin receptor and affecting itsfunction or specifically binding capsaicin receptor-related polypeptideand affecting its interaction with capsaicin receptor, thereby affectingcapsaicin receptor activity. Identification of such compounds can beaccomplished using any of a variety of drug screening techniques. Ofparticular interest is the identification of agents that have activityin affecting capsaicin receptor function. Such agents are candidates fordevelopment of treatments for, inflammatory conditions associated atleast in part with capsaicin receptor activity (e.g, psoriasis, reactiveairway diseases (e.g., asthma, chronic obstructive pulmonary disease)),arthritis (e.g., osteoarthritis, rheumatoid arthritis), and for use asanalgesics. Of particular interest are screening assays for agents thathave a low toxicity for human cells. The polypeptide employed in such atest can be free in solution, affixed to a solid support, present on acell surface, or located intracellularly. The screening assays of theinvention are generally based upon the ability of the agent to bind to acapsaicin receptor polypeptide, bind to a capsaicin receptor-relatedpolypeptide, and/or elicit or inhibit a capsaicin receptor-associated orcapsaicin receptor-related polypeptide-associated biological activity(i.e., a functional assay or an assay using radioligand binding assays).

The term “agent” as used herein describes any molecule, e.g. protein orpharmaceutical, with the capability of altering (i.e., eliciting orinhibiting) or mimicking a desired physiological function of capsaicinreceptor or capsaicin receptor-related polypeptide. Generally aplurality of assay mixtures are run in parallel with different agentconcentrations to obtain a differential response to the variousconcentrations. Typically, one of these concentrations serves as anegative control, i.e. at zero concentration or below the level ofdetection.

Candidate agents encompass numerous chemical classes, though typicallythey are organic molecules, preferably small organic compounds having amolecular weight of more than 50 and less than about 2,500 daltons.Candidate agents comprise functional groups necessary for structuralinteraction with proteins, particularly hydrogen bonding, and typicallyinclude at least an amine, carbonyl, hydroxyl or carboxyl group,preferably at least two of the functional chemical groups. The candidateagents often comprise cyclical carbon or heterocyclic structures and/oraromatic or polyaromatic structures substituted with one or more of theabove functional groups. Candidate agents are also found amongbiomolecules including, but not limited to: peptides, saccharides, fattyacids, steroids, purines, pyrimidines, derivatives, structural analogsor combinations thereof.

Candidate agents are obtained from a wide variety of sources includinglibraries of synthetic or natural compounds. For example, numerous meansare available for random and directed synthesis of a wide variety oforganic compounds and biomolecules, including expression of randomizedoligonucleotides and oligopeptides. Alternatively, libraries of naturalcompounds in the form of bacterial, fungal, plant and animal extracts(including extracts from human tissue to identify endogenous factorsaffecting capsaicin receptor or capsaicin receptor-related polypeptideactivity) are available or readily produced. Additionally, natural orsynthetically produced libraries and compounds are readily modifiedthrough conventional chemical, physical and biochemical means, and maybe used to produce combinatorial libraries. Known pharmacological agentsmay be subjected to directed or random chemical modifications, such asacylation, alkylation, esterification, amidification, etc. to producestructural analogs.

Preferably, the drug screening technique used provides for highthroughput screening of compounds having suitable binding affinity tothe capsaicin receptor, capsaicin receptor-related polypeptide, and/oreliciting a desired capsaicin receptor-associated or capsaicinreceptor-related polypeptide-associated response. For example, largenumbers of different small peptide test compounds can be synthesized ona solid substrate, such as plastic pins or some other surface (see,e.g., Geysen WO Application 84/03564, published on Sep. 13, 1984), thepeptide test compounds contacted with capsaicin receptor polypeptides(or capsaicin receptor-related polypeptides), unreacted materials washedaway, and bound capsaicin receptor (or bound capsaicin receptor-relatedpolypeptide) detected by virtue of a detectable label or detection of abiological activity associated with capsaicin receptor activity (orcapsaicin receptor-related polypeptide activity). Purified capsaicinreceptor or purified capsaicin receptor-related polypeptide can also becoated directly onto plates for use in such in vitro drug screeningtechniques. Alternatively, non-neutralizing antibodies can be used tocapture the polypeptide and immobilize it on a solid support.

The invention also contemplates the use of competitive drug screeningassays in which capsaicin receptor-specific neutralizing antibodies orcapsaicin receptor-related polypeptide-specific neutralizing antibodiescompete with a test compound for binding of capsaicin receptorpolypeptide or capsaicin receptor-related polypeptide. In this manner,the antibodies can be used to detect the presence of any polypeptidethat shares one or more antigenic determinants with a capsaicin receptorpolypeptide or capsaicin receptor-related polypeptide.

Screening of Candidate Agents

A wide variety of assays may be used for identification of capsaicinreceptor polypeptide and/or capsaicin receptor-related polypeptidebinding agents, including labeled in vitro binding assays, immunoassaysfor protein binding, and the like. For example, by providing for theproduction of large amounts of capsaicin receptor polypeptides orcapsaicin receptor-related polypeptides, one can identify ligands orsubstrates that bind to, modulate or mimic the action of the proteins.The purified protein may also be used for determination ofthree-dimensional crystal structure, which can be used for modelingintermolecular interactions.

The screening assay can be a binding assay, wherein one or more of themolecules may be joined to a label, and the label directly or indirectlyprovide a detectable signal. Various labels include radioisotopes,fluorescers, chemiluminescers, enzymes, specific binding molecules,particles, e.g. magnetic particles, and the like. Specific bindingmolecules include pairs, such as biotin and streptavidin, digoxin andantidigoxin etc. For the specific binding members, the complementarymember would normally be labeled with a molecule that provides fordetection, in accordance with known procedures.

A variety of other reagents may be included in the screening assaysdescribed herein. Where the assay is a binding assay, these includereagents like salts, neutral proteins, e.g. albumin, detergents, etcthat are used to facilitate optimal protein-protein binding, protein-DNAbinding, and/or reduce non-specific or background interactions. Reagentsthat improve the efficiency of the assay, such as protease inhibitors,nuclease inhibitors, anti-microbial agents, etc. may be used. Themixture of components are added in any order that provides for therequisite binding. Incubations are performed at any suitabletemperature, typically between 4 and 40° C. incubation periods areselected for optimum activity, but may also be optimized to facilitaterapid high-throughput screening. Typically between 0.1 and 1 hours willbe sufficient.

Functional Capsaicin Receptor and Capsaicin Receptor-Related PolypeptideScreening Assays

Preferably, capsaicin receptor-binding compounds are screened foragonistic or antagonist action in a functional assay that monitors abiological activity associated with capsaicin receptor function such aseffects upon intracellular levels of cations in a capsaicinreceptor-expressing host cell (e.g., calcium, magnesium, guanidinium,cobalt, potassium, cesium, sodium, and choline, preferably calcium),ligand-activated conductances, cell death (i.e., receptor-mediated celldeath which can be monitored using, e.g., morphological assays, chemicalassays, or immunological assays), depolarization of the capsaicinreceptor-expressing cells (e.g., using fluorescent voltage-sensitivedyes), second messenger production (e.g., through detection of changesin cyclic GMP levels (see, e.g., Wood et al. 1989 J. Neurochem.53:1203–1211), which can be detected by radioimmunoassay or ELISA),calcium-induced reporter gene expression (see, e.g., Ginty 1997 Neuron18:183–186), or other readily assayable biological activity associatedwith capsaicin receptor activity or inhibition of capsaicin receptoractivity. Preferably, the functional assay is based upon detection of abiological activity of capsaicin receptor that can be assayed usinghigh-throughput screening of multiple samples simultaneously, e.g., afunctional assay based upon detection of a change in fluorescence whichin turn is associated with a change in capsaicin receptor activity. Suchfunctional assays can be used to screen candidate agents for activity aseither capsaicin receptor agonists or antagonists.

In a preferred embodiment, capsaicin receptor-expressing cells(preferably recombinant capsaicin receptor-expressing cells) arepre-loaded with fluorescently-labeled calcium (e.g, fura-2). Thecapsaicin receptor-expressing cells are then exposed to a candidatecapsaicin receptor-binding compound and the effect of exposure to thecompound monitored. Candidate compounds that have capsaicin receptoragonist activity are those that, when contacted with the capsaicinreceptor-expressing cells, elicit a capsaicin receptor-mediated increasein intracellular calcium relative to control cells (e.g., capsaicinreceptor-expressing cells in the absence of the candidate compound, hostcells without capsaicin receptor-encoding nucleic acid, capsaicinreceptor-expressing cells exposed to a known capsaicin receptoragonist). Similarly, functional capsaicin receptor assays can be used toidentify candidate compounds that block activity of a known capsaicinreceptor agonist (e.g., block the activity of or compete with capsaicinor resiniferatoxin), block activity of a known capsaicin receptorantagonist (e.g., block the activity of or compete with capsazepine),and/or have activity as capsaicin receptor antagonists.

In another embodiment, the invention includes a method for identifyingcompounds that bind capsaicin receptor-related polypeptide, therebyeliciting an agonistic or antagonistic effect on capsaicinreceptor-associated function as detected by e.g., intracellular levelsof cations in the host cell. To this end, the functional assay involvescontacting host cells expressing a capsaicin receptor alone (e.g., VR1)and with host cell co-expressing a capsaicin receptor and a capsaicinreceptor-related polypeptide (e.g., VR1 and VRRP-1). Compounds thataffect capsaicin receptor activity by affecting function of a capsaicinreceptor-related polypeptide are those that affect a capsaicinreceptor-associated activity in cells that co-express capsaicin receptorand capsaicin receptor-related polypeptide, but do not significantlyaffect capsaicin receptor-associated activity in host cells that expresscapsaicin receptor alone. For example, compounds that elicit a capsaicinreceptor-mediated increase in intracellular calcium in cellsco-expressing capsaicin receptor and capsaicin receptor-relatedpolypeptide, but not in cells expressing capsaicin receptor alone, areidentified as compounds that elicit capsaicin receptor agonist activityvia interaction with a capsaicin receptor-related polypeptide.

Pharmaceutical Compositions and Other Compositions Comprising AgentsAffecting Capsaicin Receptor Activity Identified by the Screening Assayof the Invention

Capsaicin receptor-binding compounds and capsaicin receptor-relatedpolypeptide-binding compounds are useful in eliciting or inhibitingcapsaicin receptor-mediated physiological responses, and can beparticularly useful in a pharmaceutical composition for amelioratingsymptoms associated with chronic pain, inflammation, and otherphysiological responses associated with capsaicin receptor-mediatedactivity.

The compounds having the desired pharmacological activity may beadministered in a physiologically acceptable carrier to a host fortreatment of a condition attributable to capsaicin receptor activity.Alternatively, the identified compounds may be used to enhance,regulate, or otherwise manipulate capsaicin receptor function. Thetherapeutic agents may be administered in a variety of ways, topically,subcutaneously, intraperitoneally, intravascularly, orally,intrathecally, epidermally, intravesicularly (e.g., as in bladderirrigation to treat neurogenic bladder syndromes), parenterally, etc.Inhaled treatments are of particular interest for the treatment ofcapsaicin receptor-associated inflammation associated with suchconditions as asthma.

Depending upon the manner of introduction, the compounds may beformulated in a variety of ways. The concentration of therapeuticallyactive compound in the formulation may vary from about 0.1–100 wt. %.The pharmaceutical compositions can be prepared in various forms, suchas granules, tablets, pills, capsules, suspensions, salves, lotions andthe like. Pharmaceutical grade organic or inorganic carriers and/ordiluents suitable for the selected route of administration can be usedto make up compositions containing the therapeutically-active compounds.Diluents known to the art include aqueous media, vegetable and animaloils and fats. Stabilizing agents, wetting and emulsifying agents, saltsfor varying the osmotic pressure or buffers for securing an adequate pHvalue, and skin penetration enhancers can be used as auxiliary agents.

In addition, compositions comprising agents affecting capsaicin receptoractivity (e.g., by binding capsaicin receptor or by binding a capsaicinreceptor-related polypeptide) are useful in other applications,including use in defensive sprays (e.g., “pepper sprays”) or asantidotes for such sprays. The screening methods of the invention can beused in a variety of ways to this end, including, for example,identification of drugs that have capsaicin-like activity, but lack orare substantially diminished in one or more of the undesirable sideeffects associated with capsaicin. For example, while capsaicin iseffective in spray deterrents, exposure to capsaicin can be lethal. Thescreening method of the invention can thus be used to identify compoundsthat have the desired deterrent effect, but would not likely cause deathupon exposure to amounts normally used in defensive sprays. Moreover,the screening method of the invention could be used to identifycompounds that differentially affect capsaicin receptors of differentmammalian species, thus enabling identification and design of capsaicinreceptor agonists and antagonists that substantially affect capsaicinreceptors with genus- or species-specificity. Thus, for example, themethod of the invention can allow for identification of capsaicinreceptor agonists for canine or bear capsaicin receptors, but that donot substantially stimulate human capsaicin receptors. This could beaccomplished by screening for compounds that elicit a capsaicinreceptor-associated biological activity in host cells expressing acanine capsaicin receptor, but relatively little or no biologicalactivity in host cells expressing human capsaicin receptor.

Therapeutically Effective Dosages

The determination of an effective dose is well within the capability ofthose skilled in the art. For any compound, the therapeuticallyeffective dose can be estimated initially either in cell culture assays,e.g., using host cells expressing recombinant capsaicin receptor, or inanimal models, usually rats, mice, rabbits, dogs, or pigs. The animalmodel is also used to achieve a desirable concentration range and routeof administration. Such information can-then be used to determine usefuldoses and routes for administration in humans. A therapeuticallyeffective dose refers to that amount of an agent (e.g., a compoundhaving activity as capsaicin receptor agonist or antagonist),polypeptide, or anti-polypeptide antibody, that provide the desiredphysiological effect (e.g., to ameliorate symptoms associated withcapsaicin receptor-mediated inflammation or pain, or provide loss oftemperature sensation).

Therapeutic efficacy and toxicity of such compounds can be determined bystandard pharmaceutical procedures in cell cultures or experimentalanimals, e.g., ED50 (the dose therapeutically effective in 50% of thepopulation) and LD50 (the dose lethal to 50% of the population). Thedose ratio between therapeutic and toxic effects is the therapeuticindex, and expressed as the ratio LD50/ED50. Pharmaceutical compositionsthat exhibit large therapeutic indices are preferred. The data obtainedfrom cell culture assays and animal studies is used in formulating arange of dosage for human use. The dosage of such compounds liespreferably within a range of circulating concentrations that include theED50 with little or no toxicity. The actual dosage can vary within thisrange depending upon, for example, the dosage form employed, sensitivityof the patient, and the route of administration.

The exact dosage is chosen by the individual physician in view of thepatient to be treated. Dosage and administration are adjusted to providesufficient levels of the active moiety or to maintain the desiredeffect. Additional factors that may be taken into account include theseverity of the disease state, location of the site to be treated; age,weight and gender of the patient; diet, time and frequency ofadministration; drug combination(s); reaction sensitivities; andtolerance/response to therapy. Long-acting pharmaceutical compositionscan be administered every 3 to 4 days, every week, or once every twoweeks depending on half-life and clearance rate of the particularformulation.

Normal dosage amounts may vary depending upon the route ofadministration. Guidance as to particular dosages and methods ofdelivery is provided in the literature and generally available topractitioners in the art. Use of capsaicin and capsaicin analogues inclinical applications and their methods of administration (e.g.,formulations, dosages, routes of administration, etc.) are well known inthe art (see, e.g, Campbell et al. 1993 “Clinical Applications ofCapsaicin and Its Analogues,” in Capsaicin in the Study of Pain, pgs.255–272; U.S. Pat. No. 5,5690,910 (topical anti-inflammatorycompositions comprising capsaicin); U.S. Pat. No. 5,296,225 (topicalcomposition comprising capsaicin for treating orofacial pain); U.S. Pat.No. 5,290,816 (topical cream containing resiniferatoxin fordesensitization of neurogenic inflammation); U.S. Pat. No. 4,997,853(topical composition containing capsaicin for treating superficialpain); U.S. Pat. No. 5,403,868 (capsaicin derivatives useful asanalgesic and anti-inflammatory agents); U.S. Pat. No. 4,939,149(administration of resiniferatoxin to cause sensory afferent C-fibre andthermo-regulatory desensitization); U.S. Pat. No. 4,536,404 (topicaltreatment of post herpetic neuralgia by application of capsaicin), eachof which is incorporated by reference in its entirety. Further generalguidance on administration of capsaicin receptor agonist and antagonistscan be found in, e.g., United States Pharmacopeia (USP), 17^(th) Ed.,pgs. 710–711; and Physician's Desk Reference 1996, Medical EconomicsCorn., Montvale, N.J. (see particularly Dolorac™ at 1054, Zostrix™ at1056, and Zostrix-HP™ topical analgesic cream at 1056, each of whichcontain capsaicin); and the latest edition of Remingtons'PharmaceuticalSciences, Mack Publishing Co., Easton Pa.

Use of Capsaicin Receptor-Encoding Polynucleotides in Assays forQuantitating the Capsaicin Content of a Sample or Determining theCapsaicin Activity of a Candidate Food Additive

Capsaicin receptor polypeptide-encoding polynucleotides and capsaicinreceptor polypeptides can be used in an assay to determine, eitherqualitatively or quantitatively, to detect capsaicin or an agent havingcapsaicin activity, in a sample, where the sample is derived from a foodproduct or contains a candidate agent for use as a flavoring agent (e.g,for use as a spice in food or food products). This assay takes advantageof the fact that, in addition to its analgesic effects upon afferentneurons, capsaicin is a member of the vanilloid family of compounds,which are responsible for making foods “spicy hot.” For example,capsaicin is present in peppers (e.g., Thai. green poblano verde,habenero, and guero peppers). Conventional assays for determining theamount of capsaicin in a pepper extract involve tedious extraction ofthe compound from pepper samples and quantitation by high pressureliquid chromatography (HPLC) (see, e.g., Woodbury 1980 J. Assoc. Off.Anal. Chem. 63:556–558). The amount of capsaicin is then correlated withnumber of Scoville heat units, a measure of “hotness.”

The assay of the invention uses an isolated capsaicin receptorpolypeptide to detect the amount of capsaicin in a sample, thus avoidingthe chemical extraction technique employed in the conditional assay. Thecapsaicin receptor polypeptide used may be either bound to a solidsupport present in solution, or present on the surface of a recombinanthost cell. Binding of capsaicin to the capsaicin receptor polypeptide isdetected as described in the screening assays described above.

Preferably, the assay for capsaicin or a compound having capsaicinactivity in a sample is performed using a functional assay describedabove. More preferably, the functional assay uses capsaicinreceptor-expressing recombinant eukaryotic cells (preferably mammaliancells or amphibian oocytes) that are preloaded with a calcium-sensitivefluorescent dye (e.g., fura-2, indo-1, fluo-3). The presence and/oramount of capsaicin or capsaicinoid compound in the sample is thendetermined by measuring a capsaicin receptor-mediated cellular effect,e.g., an alteration in voltage-activated conductances across thecellular membrane or an alteration in the intracellular levels of thedetectably labeled cation. For example, where the detectably labeledcation is fluorescently labeled calcium, exposure of the pre-loaded hostcells to a capsaicin-containing sample results in binding of thecapsaicin to the capsaicin receptor polypeptide and the capsaicinreceptor-mediated increase in intracellular calcium, which can bereadily detected and quantitated. For example, the level ofintracellular calcium influx mediated by the test sample is compared tothe intracellular calcium influx associated with a control sample (e.g.,with a sample having a known amount of capsaicin). The extent of thechange in current, intracellular calcium concentration, or othercapsaicin receptor-mediated phenomenon is then correlated with aconcentration of capsaicin, which in turn can be assigned a Scovilleheat unit.

Similarly, candidate agents for use as food additives to make a food orfood product “hot” can be screened for their ability to elicit acapsaicin receptor-mediated cellular response (e.g., change in voltageactivated conductances or intracellular cation concentration). The assayhas the advantage that the measure of hotness can be determinedobjectively, e.g., based upon the responses elicited by exposure to thecapsaicin receptor.

Diagnostic Uses of Polynucleotides Encoding Capsaicin Receptor orCapsaicin Receptor-Related Polypeptides to Detect CapsaicinReceptor-Encoding Sequences

Polynucleotide sequences encoding capsaicin receptor polypeptide orcapsaicin receptor-related polypeptide can be used in the diagnosis(e.g., prenatal or post-natal diagnosis) of conditions or diseasesassociated with, for example, capsaicin receptor expression, with aparticular capsaicin receptor polymorphism or mutation, and/or withcapsaicin receptor-related polypeptide expression. For example,polynucleotide sequences encoding capsaicin receptor or capsaicinreceptor-related polypeptide can be used in hybridization or PCR assaysof fluids or tissues from biopsies to detect capsaicin receptor orcapsaicin receptor-related polypeptide expression, respectively.Suitable qualitative or quantitative methods include Southern ornorthern analysis, dot blot or other membrane-based technologies; PCRtechnologies; dip stick, pIN, chip and ELISA technologies. All of thesetechniques are well known in the art and are the basis of manycommercially available diagnostic kits. Once disease is established, atherapeutic agent is administered or other intervention or precautionsinitiated as appropriate for the capsaicin receptor-associated disorder.

Oligonucleotides based upon capsaicin receptor or capsaicinreceptor-related polypeptide sequences can be used in PCR-basedtechniques for assessing capsaicin receptor-polypeptide expression,detection of capsaicin receptor polymorphisms associated with disorders,and/or capsaicin receptor related polypeptide expression. Methods forPCR amplification are described in U.S. Pat. Nos. 4,683,195 and4,965,188. Such oligomers are generally chemically synthesized, orproduced enzymatically or by recombinantly. Oligomers generally comprisetwo nucleotide sequences, one with sense orientation (5′->3′) and onewith antisense (3′<-5′), employed under optimized conditions foridentification of a specific gene or condition. The same two oligomers,nested sets of oligomers, or even a degenerate pool of oligomers can beemployed under less stringent conditions for detection and/orquantitation of closely related DNA or RNA sequences.

Additional methods for quantitation of expression of a particularmolecule according to the invention include radiolabeling (Melby et al1993 J Immunol Methods 159:23544) or biotinylating (Duplaa C 1993 AnalBiochem 229–36) nucleotides, coamplification of a control nucleic acid,and interpolation of experimental results according to standard curves.Quantitation of multiple samples can be made more time efficient byrunning the assay in an ELISA format in which the oligomer of interestis presented in various dilutions and rapid quantitation is accomplishedby spectrophotometric or colorimetric detection.

Therapeutic Uses of Capsaicin Receptor Polypeptides and CapsaicinReceptor Polypeptide-Encoding Nucleic Acid

Polypeptides of, as well as nucleotide sequence encoding, capsaicinreceptor polypeptides and capsaicin receptor-related polypeptides may beuseful in the treatment of conditions associated with capsaicin receptordysfunction (e.g., capsaicin receptor activity that is increasedrelative to capsaicin receptor activity in an unaffected patient orcapsaicin receptor activity that is decreased relative to capsaicinreceptor activity in an unaffected patient). In addition, expression ofdominant-negative capsaicin receptor-encoding sequences may betherapeutically useful in a condition associated with elevated levels ofcapsaicin receptor activity. Where interaction of capsaicin receptor anda capsaicin receptor-related polypeptide is associated with a condition,interaction of these polypeptides can be disrupted by, for example,introduction of a peptide corresponding to an interaction domain ofcapsaicin receptor and capsaicin receptor-related polypeptide. Moreover,expression of a wild-type capsaicin receptor sequence in tumor cells mayrender such tumor cells more susceptible to capsaicin receptor-mediatedcell death.

Expression vectors derived from retroviruses, adenovirus, herpes orvaccinia viruses, or from various bacterial plasmids, can be used fordelivery of nucleotide sequences to the targeted organ, tissue or cellpopulation. Preferably the targeted cell for delivery and expression ofcapsaicin receptor polypeptide-encoding sequences is a neuronal cell,more preferably an afferent neuron in order to enhance capsaicinreceptor activity in the neuronal cell. Recombinant vectors forexpression of antisense capsaicin receptor polynucleotides can beconstructed according to methods well known in the art (see, forexample, the techniques described in Sambrook et al (supra) and Ausubelet al (supra)).

Alternatively, expression of genes encoding capsaicin receptor can bedecreased by transfecting a cell or tissue with expression vectors thatexpress high levels of a desired capsaicin receptor-encoding fragment.Such constructs can flood cells with untranslatable sense or antisensesequences. Even in the absence of integration into the DNA, such vectorscan continue to transcribe RNA molecules until all copies are disabledby endogenous nucleases. Such an approach to regulation of capsaicinreceptor expression and activity can be useful in treatment of painsyndromes and/or inflammatory conditions associated with capsaicinreceptor activity.

Modifications of gene expression can be obtained by designing antisensemolecules, DNA, RNA or PNA, to the control regions of gene encodingcapsaicin receptor (i.e., the promoters, enhancers, and introns).Oligonucleotides derived from the transcription initiation site, e.g.,between −10 and +10 regions of the leader sequence, are preferred. Theantisense molecules can also be designed to block translation of mRNA bypreventing the transcript from binding to ribosomes. Similarly,inhibition of expression can be achieved using “triple helix”base-pairing methodology. Triple helix pairing compromises the abilityof the double helix to open sufficiently for binding of polymerases,transcription factors, or regulatory molecules. Recent therapeuticadvances using triplex DNA were reviewed by Gee J E et al (In: Huber etal. 1994 Molecular and Immunologic Approaches, Futura Publishing Co, MtKisco N.Y.). Antisense molecules of the invention can be prepared bymethods known in the art for the synthesis of RNA molecules, includingtechniques for chemical oligonucleotide synthesis, e.g., solid phasephosphoramidite chemical synthesis. Such DNA sequences can beincorporated into a wide variety of vectors with suitable RNA polymerasepromoters (e.g, T7 or SP6). Alternatively, antisense cDNA constructsuseful in the constitutive or inducible synthesis of antisense RNA canbe introduced into cell lines, cells, or tissues.

Particularly where RNA molecules are to be administered for antisensetherapy, the RNA can be modified to increase intracellular stability andhalf-life. Possible modifications include, but are not limited to, theaddition of flanking sequences at the 5′ and/or 3′ ends of the molecule,or the use of phosphorothioate or 2′ O-methyl rather thanphosphodiesterase linkages within the backbone of the molecule. Thisconcept is inherent in the production of PNAs and can be extended in allof these molecules by the inclusion of nontraditional bases such asinosine, queosine and wybutosine as well as acetyl-, methyl-, thio- andsimilarly modified forms of adenine, cytidine, guanine, thymine, anduridine that are not as easily recognized by endogenous endonucleases.

Methods for introducing vectors into cells or tissues include thosemethods discussed infra and which are equally suitable for in vivotherapy.

In a preferred embodiment, capsaicin receptor polypeptide-encodingpolynucleotides are introduced in vivo into a target tumor cell forwhich organochemotherapy is desired. This aspect of the invention takesadvantage of the range of capsaicin receptor response to exposure toagonists (e.g, capsaicin, resiniferatoxin) and/or to temperature. Forexample, low concentrations of capsaicin receptor agonists (e.g.,capsaicin receptor agonist concentrations in the nanomolar range, e.g,from about 200 nM to about 800 nM are associated with capsaicin receptorstimulation and intracellular calcium influx. Where the capsaicinreceptor is expressed in a neuronal cell, capsaicin receptor stimulationby low concentrations of capsaicin receptor agonist is followed byneuronal desensitization. However, high concentrations of capsaicinreceptor agonists (e.g., capsaicin receptor agonist concentrations inthe micromolar range, e.g., from about 1 μM to about 10 μM mediateneuronal degeneration and cell death. By expressing capsaicin receptorpolypeptides in tumor cells, the tumor cell death can be substantiallyselectively facilitated by local administration of high concentrationsof a capsaicin receptor agonist, or by local exposure to heat stimuli,or both, where the agonist concentration and/or heat stimulus issufficient to mediate cell death in the capsaicin receptor-expressingtarget tumor cell, but does not substantially affect normal capsaicinreceptor-expressing cells or affects a minimal number of such normalcells.

Alternatively, the capsaicin receptor polypeptide introduced into thetumor cells can be engineered to provide more selectivity in theresponse to organochemotherapy (i.e., to provide for activation of thecapsaicin receptor expressed in the tumor cells with no or littleactivation of endogenous, wild-type capsaicin receptor). For example,capsaicin receptor can be modified so as to bind a specific capsaicinreceptor agonist analogue, which analogue is substantially reduced inits ability to bind wildtype capsaicin receptors. Therefore, targetcells (e.g, tumor cells) expressing the altered capsaicin receptor canbe selectively stimulated by administration of the agonist havingspecificity for the altered capsaicin receptor polypeptide withoutsubstantially affecting cells expressing wildtype capsaicin receptor.Alternatively, the tumor cells can be transformed in vivo with asequence encoding a modified capsaicin receptor, where the modifiedcapsaicin receptor is more responsive to agonists (e.g., is moreresponsive to agonist, has increased affinity to agonists relative towild-type thereby allowing activation of the modified receptors with noor little activation of the endogenous capsaicin receptor, and/or ismodified so as to be more responsive to heat stimuli than wild-typecapsaicin receptor). These embodiments thus allow administration of highor higher concentrations of the altered capsaicin receptor-targetedorganochemotherapeutic, thereby providing for more selectiveorganochemotherapy.

Anti-Capsaicin Receptor and Anti-Capsaicin Receptor-Related PolypeptideAntibodies

Capsaicin receptor-specific antibodies and capsaicin receptor-relatedpolypeptide-specific antibodies are useful for identification of cellsexpressing either naturally-occurring or recombinant capsaicin receptorpolypeptides or capsaicin receptor-related polypeptides, respectively,as well as the diagnosis of conditions and diseases associated withexpression and/or function of capsaicin receptor and/or capsaicinreceptor-related polypeptides. For example, ant-capsaicin receptorantibodies and anti-capsaicin receptor-related polypeptide antibodiescan be used to detect increased or decreased receptor protein levels,and/or aberrant protein processing or oligomerization.

Anti-capsaicin receptor polypeptide antibodies and ant-capsaicinreceptor-related polypeptide antibodies of the invention include, butare not limited to, polyclonal, monoclonal, chimeric, single chain, Fabfragments and fragments produced by a Fab expression library. Antibodiesof particular interest include, for example, antibodies that stimulatecapsaicin receptor function and/or block binding of capsaicinreceptor-binding compounds to capsaicin receptor. Such antibodies may beuseful in, for example, regulation of pain in pain syndromes, inscreening assays for capsaicin receptor-binding agents, and inmeasurement of capsaicin receptor-activating compounds in a sample.

Capsaicin receptor polypeptides and capsaicin receptor-relatedpolypeptides suitable for production of antibodies need not bebiologically active; rather, the polypeptide, or oligopeptide need onlybe antigenic. Polypeptides used to generate capsaicin receptor-specificantibodies and capsaicin receptor-related polypeptide antibodiesgenerally have an amino acid sequence consisting of at least five aminoacids, preferably at least 10 amino acids. Preferably, antigeniccapsaicin receptor polypeptides and antigenic capsaicin receptor-relatedpolypeptides mimic an epitope of the native capsaicin receptor or nativecapsaicin receptor-related polypeptide, respectively. Antibodiesspecific for short polypeptides can be generated by linking thecapsaicin receptor polypeptide or capsaicin receptor-related polypeptideto a carrier, or fusing the capsaicin receptor polypeptide or capsaicinreceptor-related polypeptide to another protein (e.g., keyhole limpethemocyanin), and using the carrier-linked chimeric molecule as anantigen. In general, anti-capsaicin receptor antibodies and capsaicinreceptor-related polypeptide antibodies can be produced according tomethods well known in the art Recombinant immunoglobulins can beproduced as according to U.S. Pat. No. 4,816,567, incorporated herein byreference.

Various hosts, generally mammalian or amphibian hosts, can be used toproduce anti-capsaicin receptor antibodies and anti-capsaicinreceptor-related polypeptide antibodies (e.g., goats, rabbits, rats,mice). In general, antibodies are produced by immunizing the host (e.g.,by injection) with a capsaicin receptor polypeptide or capsaicinreceptor-related polypeptide that retains immunogenic properties (whichencompasses any portion of the native polypeptide, fragment oroligopeptide). Depending on the host species, various adjuvants can beused to increase the host's immunological response. Such adjuvantsinclude but are not limited to, Freund's, mineral gels (e.g., aluminumhydroxide), and surface active substances such as lysolecithin, pluronicpolyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanin,and dinitrophenol. BCG (bacilli Calmette-Guerin) and Corynebacteriumparvum are potentially useful human adjuvants.

Monoclonal antibodies can be prepared using any technique that providesfor the production of antibody molecules by immortalized cell lines inculture. These techniques include, but are not limited to, the hybridomatechnique originally described by Koehler and Milstein (1975 Nature256:495–497), the human B-cell hybridoma technique (Kosbor et al (1983)Immunol Today 4:72; Cote et al (1983) Proc Natl Acad Sci 80:2026–2030)and the EBV-hybridoma technique (Cole et al (1985) Monoclonal Antibodiesand Cancer Therapy, Alan R Liss Inc, New York N.Y., pp 77–96).

In addition techniques developed for the production of “chimericantibodies”, the splicing of mouse antibody genes to human antibodygenes to obtain a molecule with appropriate antigen specificity andbiological activity can be used (Morrison et al 1984 Proc Natl Acad Sci81:6851–6855; Neuberger et al 1984 Nature 312:604–608; Takeda et al 1985Nature 314:452–454). Alternatively, techniques described for theproduction of single chain antibodies (U.S. Pat. No. 4,946,778) can beadapted to produce-single chain antibodies that are capsaicinreceptor-specific or capsaicin receptor-related polypeptide-specific.

Antibodies can be produced in vivo or by screening recombinantimmunoglobulin libraries or panels of highly specific binding reagentsas disclosed in Orlandi et al (1989, Proc Natl Acad Sci 86: 3833–3837),and Winter et al. (1991; Nature 349:293–299).

Antibody fragments having specific binding sites for a capsaicinreceptor polypeptide or capsaicin receptor-related polypeptide can alsobe generated. For example, such fragments include, but are not limitedto, F(ab′)2 fragments, which can be produced by pepsin digestion of theantibody molecule, and Fab fragments, which can be generated by reducingthe disulfide bridges of the F(ab′)2 fragments. Alternatively, Fabexpression libraries can be constructed to allow rapid and easyidentification of monoclonal Fab fragments with the desired specificity(Huse et al 1989 Science 256:1275–1281).

A variety of protocols for competitive binding or immunoradiometricassays using either polyclonal or monoclonal antibodies havingestablished antigen specificities are well known in the art Suchimmunoassays typically involve, for example, the formation of complexesbetween a capsaicin receptor polypeptide and a specific anti-capsaicinreceptor antibody, and the detection and quantitation of capsaicinreceptor-antibody complex formation. A two-site, monoclonal-basedimmunoassay utilizing monoclonal antibodies reactive to twononinterfering epitopes on a specific capsaicin receptor protein ispreferred, but a competitive binding assay can also be employed. Theseassays are described in Maddox et al 1983, J Exp Med 158:1211.

Diagnostic Assays Using Capsaicin Receptor-Specific or CapsaicinReceptor-Related Polypeptide-Specific Antibodies

Particular capsaicin receptor antibodies and capsaicin receptor-relatedpolypeptide antibodies are useful for the diagnosis of conditions ordiseases characterized by abnormal expression or function of capsaicinreceptor (e.g., detection of capsaicin receptor expression in skin todetect neuropathies or in assays to monitor patients having a capsaicinreceptor-associated disorder or condition and/or being treated withcapsaicin receptor agonists, antagonists, or inhibitors). For example,aberrant carp function might result from over- or under-production of acapsaicin receptor-related polypeptide; thus anti-capsaicinreceptor-related antibodies can be used to detect these changesqualitatively or quantitatively. Diagnostic assays for capsaicinreceptor or capsaicin receptor-related polypeptide include methods usinga detectably-labeled anti-capsaicin receptor antibody or anti-capsaicinreceptor-related polypeptide to detect capsaicin receptor in samples(e.g., extracts of cells or tissues). The polypeptides and antibodies ofthe present invention can be used with or without modification.Frequently, the polypeptides and antibodies are labeled by covalent ornon-covalent attachment to a reporter molecule. A wide variety of suchsuitable reporter molecules are known in the art Methods for detectingand quantitating antibody binding are well known in the art.

Pharmaceutical Compositions Containing Capsaicin Receptor Polypeptides,Capsaicin Receptor-Related Polypeptides, and/or Antibodies Thereto

The present invention also encompasses pharmaceutical compositions thatcan comprise capsaicin receptor polypeptides, anti-capsaicin receptorpolypeptide antibodies, capsaicin receptor-related polypeptides, oranti-capsaicin receptor-related polypeptides, alone or in combinationwith at least one other agent, such as a stabilizing compound, which canbe administered in any sterile, biocompatible pharmaceutical carrier.The pharmaceutical compositions of the invention can be administered toa patient alone or in combination with other agents, drugs or hormones,in pharmaceutical compositions where it is mixed with excipient(s), orwith pharmaceutically acceptable carriers. In one embodiment of thepresent invention, the pharmaceutically acceptable carrier ispharmaceutically inert.

Capsaicin receptor polypeptides and/or capsaicin receptor-relatedpolypeptides can be administered in order to mitigate the effects of,for example, an endogenous factor that acts as a capsaicin receptoragonist or antagonist or to block or regulate the effects of a capsaicinreceptor agonist or antagonist administered to an individual.Anti-capsaicin receptor polypeptide antibodies and/or anti-capsaicinreceptor-related polypeptide antibodies can be administered to stimulatea capsaicin receptor in a desired fashion or to block the effects of anendogenous or exogenous capsaicin receptor-binding agonist orantagonist, e.g., via competitive binding to the capsaicin receptor.Pharmaceutical formulations comprising capsaicin receptor polypeptides,capsaicin receptor-related polypeptides, anti-capsaicin receptorantibodies, and/or anti-capsaicin receptor-related polypeptideantibodies can be formulated according to methods known in the art.

Transgenic Animals Expressing Polynucleotides Encoding CapsaicinReceptor and/or Capsaicin Receptor-Related Polypeptide

Nucleic acids encoding capsaicin receptor and/or nucleic acids encodingcapsaicin receptor-related polypeptide can be used to generategenetically modified non-human animals or site specific genemodifications in cell lines. The term “transgenic” is intended toencompass genetically modified animals having, for example, a deletionor other knock-out of capsaicin receptor gene activity (and/or capsaicinreceptor-related polypeptide activity), an exogenous capsaicin receptorgene (or capsaicin receptor-related polypeptide gene) that is stablytransmitted in the host cells, a “knock-in” having altered capsaicinreceptor (and/or capsaicin receptor-related polypeptide) geneexpression, or an exogenous capsaicin receptor or capsaicinreceptor-related polypeptide promoter operably linked to a reportergene. Of particular interest are homozygous and heterozygous knock-outsand knock-ins of capsaicin receptor and/or capsaicin receptor-relatedpolypeptide function.

Transgenic animals may be made through homologous recombination, wherethe endogenous capsaicin receptor locus (and/or capsaicinreceptor-related polypeptide locus) is altered. Alternatively, a nucleicacid construct is randomly integrated into the genome. Vectors forstable integration include plasmids, retroviruses and other animalviruses, YACs, and the like. Of interest are transgenic mammals,preferably a mammal from a genus selected from the group consisting ofMus (e.g., mice), Rattus (e.g., rats), Oryctologus (e.g., rabbits) andMesocricetus (e.g., hamsters).

A “knock-out” animal is genetically manipulated to substantially reduce,or eliminate endogenous capsaicin receptor function (and/or capsaicinreceptor-related polypeptide function). Different approaches may be usedto achieve the “knock-out”. For example, a chromosomal deletion of allor part of the native capsaicin receptor homolog (or native capsaicinreceptor-related polypeptide homolog) may be induced. Deletions of thenon-coding regions, particularly the promoter region, 3′ regulatorysequences, enhancers, or deletions of gene that activate expression ofthe capsaicin receptor gene and/or the capsaicin receptor-relatedpolypeptide gene. A functional knock-out may also be achieved by theintroduction of an anti-sense construct that blocks expression of thenative gene(s) (for example, see Li and Cohen (1996) Cell 85:319–329).

Conditional knock-outs of capsaicin receptor gene function (and/orcapsaicin receptor-related polypeptide gene function) are also includedwithin the present invention. Conditional knock-outs are transgenicanimals that exhibit a defect in capsaicin receptor gene function(and/or capsaicin receptor-related polypeptide gene function) uponexposure of the animal to a substance that promotes target genealteration, introduction of an enzyme that promotes recombination at thetarget gene site (e.g., Cre in the Cre-IoxP system), or other method fordirecting the target gene alteration.

For example, a transgenic animal having a conditional knock-out ofcapsaicin receptor gene function can be produced using the Cre-IoxPrecombination system (see, e.g., Kilby et al. 1993 Trends Genet9:413–421). Cre is an enzyme that excises the DNA between tworecognition sequences, termed IoxP. This system can be used in a varietyof ways to create conditional knock-outs of capsaicin receptor. Forexample, two independent transgenic mice can be produced: one transgenicfor an capsaicin receptor sequence flanked by IoxP sites and a secondtransgenic for Cre. The Cre transgene can be under the control of aninducible or developmentally regulated promoter (Gu et al. 1993 Cell73:1155–1164; Gu et al. 1994 Science 265:103–106), or under control of atissue-specific or cell type-specific promoter (e.g., a neuron-specificpromoter). The capsaicin receptor transgenic is then crossed with theCre transgenic to produce progeny deficient for the capsaicin receptorgene only in those cells that expressed Cre during development.

Transgenic animals may be made having an exogenous capsaicin receptorgene and/or exogenous capsaicin receptor-related polypeptide gene. Theexogenous gene is usually either from a different species than theanimal host, or is otherwise altered in its coding or non-codingsequence. The introduced gene may be a wild-type gene, naturallyoccurring polymorphism, or a genetically manipulated sequence, forexample those previously described with deletions, substitutions orinsertions in the coding or non-coding regions. The introduced sequencemay encode an capsaicin receptor polypeptide and/or capsaicinreceptor-related polypeptide. Where the introduced gene is a codingsequence, it is usually operably linked to a promoter, which may beconstitutive or inducible, and other regulatory sequences required forexpression in the host animal.

Specific constructs of interest include, but are not limited to,anti-sense polynucleotides encoding capsaicin receptor or capsaicinreceptor-related polypeptide, or a ribozyme based on a capsaicinreceptor or capsaicin receptor-related polypeptide sequence, which willblock capsaicin receptor expression or capsaicin receptor-relatedpolypeptide expression, respectively. Such ant-sense polynucleotides orribozymes will also block expression of dominant negative mutations andover-expression of the corresponding gene. Also of interest is theexpression of constructs encoding capsaicin receptor or capsaicinreceptor-related polypeptides in a host where the capsaicin receptorand/or capsaicin receptor-related polypeptide encoded by the constructis derived from a different species than the species of the host inwhich it is expressed (e.g., expression of human capsaicin receptor in atransgenic mouse). A detectable marker, such as lac Z may be introducedinto the capsaicin receptor or capsaicin receptor-related polypeptidelocus, where upregulation of expression of the corresponding gene willresult in an easily detected change in phenotype. Constructs utilizing apromoter region of the capsaicin receptor gene or capsaicinreceptor-related polypeptide gene in combination with a reporter geneare also of interest. Constructs having a sequence encoding a truncatedor altered (e.g, mutated) capsaicin receptor or capsaicinreceptor-related polypeptide are also of interest.

The modified cells or animals are useful in the study of function andregulation of capsaicin receptor and capsaicin receptor-relatedpolypeptide. Such modified cells or animals are also useful in, forexample, the study of the function of capsaicin receptor and capsaicinreceptor-related polypeptides, as well as the study of the developmentof nociceptive neurons. Animals may also be used in functional studies,drug screening, etc., e.g. to determine the effect of a candidate drugon capsaicin receptor function or on symptoms associated with disease orconditions associated with capsaicin receptor function (e.g., capsaicinreceptor defects or other altered capsaicin receptor activity). Byproviding expression of capsaicin receptor polypeptide and/or capsaicinreceptor-related polypeptide in cells in which it is otherwise notnormally produced (e.g., ectopic expression), one can induce changes incell behavior.

DNA constructs for homologous recombination will comprise at least aportion of the capsaicin receptor gene (or capsaicin receptor-relatedpolypeptide gene) with the desired genetic modification, and willinclude regions of homology to the target locus. DNA constructs forrandom integration need not include regions of homology to mediaterecombination. Conveniently, markers for positive and negative selectionare included. Methods for generating cells having targeted genemodifications through homologous recombination are known in the art. Forvarious techniques for transfecting mammalian cells, see Keown et al.1990 Methods in Enzymology 185:527–537.

For embryonic stem (ES) cells, an ES cell line may be employed, orembryonic cells may be obtained freshly from a host, e.g. mouse, rat,guinea pig, etc. Such cells are grown on an appropriatefibroblast-feeder layer or grown in the presence of appropriate growthfactors, such as leukemia inhibiting factor (LIF). When ES cells havebeen transformed, they may be used to produce transgenic animals. Aftertransformation, the cells are plated onto a feeder layer in anappropriate medium. Cells containing the construct may be detected byemploying a selective medium. After sufficient time for colonies togrow, they are picked and analyzed for the occurrence of homologousrecombination or integration of the construct. Those colonies that arepositive may then be used for embryo manipulation and blastocystinjection. Blastocysts are obtained from 4 to 6 week old superovulatedfemales. The ES cells are trypsinized, and the modified cells areinjected into the blastocoel of the blastocyst. After injection, theblastocysts are returned to each uterine horn of pseudopregnant females.Females are then allowed to go to term and the resulting littersscreened for mutant cells having the construct. By providing for adifferent phenotype of the blastocyst and the ES cells, chimeric progenycan be readily detected.

The chimeric animals are screened for the presence of the modified gene.Chimeric animals having the modification (normally chimeric males) aremated with wildtype animals to produce heterozygotes, and theheterozygotes mated to produce homozygotes. If the gene alterationscause lethality at some point in development, tissues or organs can bemaintained as allogeneic or congenic grafts or transplants, or in invitro culture.

Investigation of genetic function may utilize non-mammalian models,particularly using those organisms that are biologically and geneticallywell-characterized, such as C. elegans, D. melanogaster and S.cerevisiae. For example, transposon (Tc1) insertions in the nematodehomolog of a capsaicin receptor gene or a promoter region of a capsaicinreceptor gene may be made. The capsaicin receptor gene sequences may beused to knock-out or to complement defined genetic lesions in order todetermine the physiological and biochemical pathways involved infunction of neuronal cells. It is well known that human genes cancomplement mutations in lower eukaryotic models.

Biosensor Membranes Having Capsaicin Receptor Polypeptides

Due to the responsiveness of capsaicin receptor polypeptides to heat,capsaicin receptor polypeptides can be used in a biosensor for detectionof changes in temperature. The biosensor utilizes electchemicalmeasurement of an ion current across a lipid membrane (or other medium)having a capsaicin receptor polypeptide incorporated therein. Uponstimulation of the capsaicin receptor polypeptide by heat, the capsaicinreceptor polypeptide facilitates movement of ions (e.g., calcium) acrossthe membrane, which is then detected as a change in current across thelipid bilayer. The temperature and/or change in temperature can becorrelated with the relative increase in conductance across the bilayerdue to capsaicin receptor polypeptide activation.

It is well known that amphiphilic molecules can be caused to aggregatein solution to form two or three dimensional ordered arrays such asmonolayers, micelles, black lipid membranes, and vesicles or liposomes,which vesicles may have a single compartment or may be of themultilamellar type having a plurality of compartments. The membrane maycontain any suitable combination of lipids, long-chain (C12–C24) organiccompounds, as well as plastic materials or like polymers for physicalreinforcement. Methods and compositions for manufacture of lipidbilayers incorporating a protein of interest, as well as methods andcompositions for manufacture of the electrical and mechanical componentsof biosensors are well known in the art (see, e.g., U.S. Pat. No.5,328,847 (thin membrane sensor with biochemical switch); U.S. Pat. No.5,443,955 (receptor membranes and ionophore gating); U.S. Pat. No.5,234,566 (sensitivity and selectivity of ion channel biosensormembranes); U.S. Pat. No. 5,074,977 (digital biosensors and method ofusing same); and U.S. Pat. No. 5,156,810 (biosensors employingelectrical, optical, and mechanical signals), each of which are herebyincorporated by reference for manufacture and use of biosensorsincorporating a receptor of interest (i.e., capsaicin receptor).

Biosensors according to the present invention comprise at least onelipid membrane, where the membrane includes at least one capsaicinreceptor polypeptide. Because capsaicin receptor polypeptides canfunction when contacted with ligand (e.g., capsaicin) or other effectorthat mediates capsaicin receptor activity (e.g., heat), the orientationof capsaicin receptor in the membrane is not substantially important forthe function of the biosensor.

Conventional microelectronic configurations will serve adequately tosupply power for the sensor, provide a constant direct current voltageacross the bilayer prior to heat detection, and measure the ion currentsurge following capsaicin receptor activation elicited by a change intemperature. It may be additionally desirable to incorporate into thedetection electronics a provision for membrane integrity determination,based on the electrical noise accompanying a triggered current signal.

In general, heat is detected using the biosensor of the invention bydetecting a change in conductance across the capsaicin receptorpolypeptide-containing bilayer. For example, the capsaicin receptorpolypeptide lipid bilayer is provided so that a first face of the lipidbilayer (the “heat detection face”) is in contact with an buffersolution of neutral pH and containing a selected cation that is capableof transport by the capsaicin receptor (e.g., any cation such as calciumor magnesium, preferably sodium), while a second face of the capsaicinreceptor polypeptide lipid bilayer is in contact with a neutral pHbuffer having a concentration of the selected cation that issignificantly less than the concentration of selected cation in thebuffer bathing the heat detection face of the bilayer. Upon exposure ofthe bilayer's heat detection face to a change in temperature, heatfacilitates capsaicin receptor function to provide for transport of theselected cation across the bilayer, resulting in a change in conductanceacross the bilayer. The change in conductance is then correlated with achange in temperature.

The examples below are provided to illustrate the subject invention andare not included for the purpose of limiting the invention.

EXAMPLES Example 1 Expression Cloning of Rat Capsaicin Receptor-EncodingDNA

While electrophysiological assays in Xenopus oocytes have been employedto obtain cDNAs encoding a variety of cell surface receptors and ionchannels (Brake et al. 1995 Nature 371:519–523), this approach provedunsuccessful in identifying a capsaicin receptor clone. A mammalian cellexpression cloning strategy based on the ability of capsaicin to triggeran influx of calcium ions into sensory neurons was developed. First, arodent dorsal root ganglion plasmid cDNA library was constructed inpcDNA3 (Invitrogen) essentially as described (Brake et al., supra). Amixture of polyadenylated RNA from newborn (P1) rat and adult mousedorsal root ganglia was used to generate first-strand cDNA using anoligo (dT) primer containing a Not1 restriction site. Following secondstrand synthesis and attachment of BstX1 adaptors, the cDNA was digestedwith Not1. cDNA and BstX1/Not1-linearized pcDNA3 were each purified onpotassium acetate gradients, ligated together, and transformed in DH5αbacteria by electroporation. The resulting 2.4×10⁶ independent bacterialclones were divided into 144 pools and stored at −80° C.

HEK 293 (human embryonal kidney) cells constitutively expressing theSV40 large T antigen were maintained in Medium A (DMEM supplemented with10% fetal bovine serum (Hyclone), penicillin, streptomycin, andL-glutamine) at 37° C., 5% CO₂. Except where indicated, transienttransfections were carried out with nearly-confluent cells that werereplated at 3.2×10⁵/35 mm tissue culture dish. After 24 hrs, the mediumwas replaced with 1 ml Medium B (DMEM supplemented with 10% dialyzedfetal calf serum, penicillin, streptomycin, and L-glutamine). After 2hrs at 37° C., cells were transfected with 12 μg plasmid DNA using acalcium phosphate precipitation kit (Specialty Media). The followingday, cells were rinsed once with phosphate buffered saline (PBS)containing 1 mM EDTA, washed from the plates, collected bycentrifugation (200×g, 5 min, 22° C.), resuspended in Medium B, andre-plated onto polyomithine-coated coverslips. Under these conditions,each cell acquired plasmids encoding approximately 200 different cDNAs.

Between 6 and 24 hours later, cells were loaded with fura2 (30 min at37° C.) in CIB buffer (mM: 130 NaCl, 3 KCl, 2.5 CaCl₂, 0.6 MgCl₂, 1.2NaHCO₃, 10 Glucose, 10 Hepes, pH 7.45) containing 10 μM fura-2acetoxymethyl ester and 0.02% pleuronic acid (Molecular Probes), thenrinsed twice with CIB. Ratiometric calcium imaging was performed using aNikon Diaphot fluorescence microscope equipped with a variable filterwheel (Sutter Instruments) and an intensified CCD camera (Hamamatsu).Dual images (at 340 nm and 380 nm excitation, 510 nm emission) werecollected and pseudocolor ratiometric images monitored during theexperiment (Metafluor imaging software, Universal Imaging). Cells wereinitially imaged in 200 ml CIB, after which 200 ml CIB containingcapsaicin at twice the desired concentration was added. Followingstimuli, cells were observed for 60–120 s. For each library pool, onemicroscopic field (300–500 cells) was assayed in each of eight wells.

While cells transfected with most of the assayed pools or with pcDNA3alone exhibited no capsaicin responsiveness, 1% to 5% of the cellstransfected with one of the cDNA library pools exhibited a profoundincrease in cytoplasmic calcium concentrations upon capsaicin treatmentcDNA from this pool was further subdivided into smaller pools, and thosesubpools retransfected into HEK293 cells. In cell populationstransfected with some of these subpools, an even larger fraction ofcells responded to capsaicin, indicating that a capsaicinreceptor-encoding cDNA had been enriched within the population. Theprocess of pool subdivision and reassay was continued until a singleplasmid was isolated that conferred capsaicin-responsiveness upon greatthan 70% of the transfected cells. The clone that conferredcapsaicin-responsiveness contained a 3 kb cDNA insert.

Example 2 Sequencing and Characterization of Capsaicin Receptor-EncodingcDNA

The 3 kb cDNA insert was sequenced using an automated sequencer (ABI).Homology searches were performed against the nonredundant Genbankdatabase and against an EST database (dbest) using blastn, blastx, andtblastx search programs. Hydrophilicity was calculated using theHopp-Woods algorithm and a window size of ten 47. The insert wasdetermined to be of rat origin by sequencing an independent cDNAisolated from a rat DRG library and a PCR product derived from mouse DRGcDNA. The sequence of the isolated rat capsaicin receptor-encodingpolynucleotide (SEQ ID NO:1) and its corresponding amino acid sequence(SEQ ID NO:2) are shown in FIG. 1. Because a vanilloid moietyconstitutes an essential chemical component of capsaicin andresiniferatoxin structures, the proposed site of action of thesecompounds is more generally referred to as the vanilloid receptor(Szallasi 1994 Gen. Pharmac. 25:223–243). Accordly, the newly clonedcDNA was termed VR1, for vanilloid receptor subtype 1. The term“capsaicin-receptor” as used herein encompasses VR1, but is not limitedto VR1.

The VR1-encoding cDNA contains a 2514-nucleotide open reading frameencoding a protein of 838 amino acids with a predicted molecular mass of95 kD (FIGS. 1 and 2A). Hydrophilicity analysis suggests that VR1 is apolytopic protein containing 6 transmembrane domains (noted as “TM” andshaded boxes in FIG. 1 and predicted to be mostly β-sheet (see FIG. 1B))with an additional short hydrophobic stretch between transmembraneregions 5 and 6 (light shaded region). The amino-terminal hydrophilicsegment (432 aa) contains a relatively proline-rich region followed by 3ankyrin repeat domains (open boxes). The carboxyl-terminus (154 aa)contains no recognizable motifs.

A homology search of protein databases revealed significant similaritiesbetween VR1 and members of the family of putative store-operated calciumchannels (SOCs) whose prototypical members include the drosophilaretinal proteins TRP and TRPL 32, 33 (FIG. 1C). Members of this familyhave been proposed to mediate the entry of extracellular calcium intocells in response to the depletion of intracellular calcium stores 34.These proteins resemble VR1 with respect to their predicted topologicalorganization and the presence of multiple amino-terminal ankyrin repeats33. There is also striking amino acid sequence similarity between VR1and SOCs within and adjacent to the sixth transmembrane region,including the short hydrophobic region between transmembrane domains 5and 6 that may contribute to the ion permeation path 33. Outside theseregions, VR1 shares little sequence similarity with SOCs, suggestingthat VR1 is a distant relative of this family of channel proteins. Giventhe high permeability of VR1 to calcium ions, we nonetheless consideredthe possibility that it might function as a SOC.

An expressed sequence tag (EST) database homology search revealedseveral human clones bearing a high degree of similarity to VR1 at boththe nucleotide and predicted amino acid levels (FIG. 1C). Three of thesepartial cDNAs, independently isolated from different sources, encodesequences in the vicinity of the predicted VR1 pore-loop and sixthtransmembrane domains. As shown in FIG. 2C, the similarity of one ofthese clones (hVR, Genbank accession T12251) to the corresponding regionof VR1 is extremely high (68% amino acid identity and 84% similaritywithin the region shown), suggesting that it is likely to be the humanVR1 orthologue or a closely related subtype. Human EST clonescorresponding to other domains of VR1 show comparable degrees ofsimilarity (not shown) and could represent fragments of the same humantranscript.

Example 3 VR1 does not Function as a Store-Operated Calcium Channel(SOC)

The amino acid sequence similarities between VR1 and SOCs suggested thatthe capsaicin receptor might function as an SOC. To test this,calcium-dependent inward currents were examined in VR1-expressing,intracellular calcium-depleted oocytes according to methods well knownin the art.

Briefly, cRNA transcripts were synthesized from Not1— linearized VR1cDNA templates using T7 RNA polymerase 17. Defolliculated Xenopus laevisoocytes were injected with 0.5–5 ng VR1 cRNA. Four to seven days afterinjection, two electrode voltage clamp recording was performed(E_(hold)=−60 mV for IC₅₀ curve and thermal stimulation experiments and−40 mV for all other experiments) using a Geneclamp 500 amplifier (AxonInstruments) and a MacLab A/D converter (Maclab). The recording chamberwas perfused at a rate of 2 ml/min with frog ringers solution containing(mM) 90 NaCl; 1.0 KCl, 2.4 NaHCO₃, 0.1 BaCl₂, 1.0 MgCl₂, and 10 HEPES,pH 7.6. at room temperature. Prior to performing the store-operatedcurrent assays, oocytes were incubated for 1–2 hrs in calcium-free,barium-free frog ringer's solution containing 1 mM EGTA and 1 μMThapsigargin. During voltage clamp recording, these oocytes wereintermittently exposed to frog ringer's solution containing 2 mM Ca2+and no EGTA to detect calcium-dependent currents (15 second pulses at 2minute intervals) (Petersen et al. 1995 Biochem J. 311:41–44).

In water-injected control oocytes, a clear depletion-induced current wasseen, as previously described (Petersen et al., supra). InVR1-expressing oocytes, no quantitative or qualitative differences wereobserved in this response (not shown). Moreover, application of SKF96365 (20 μM), and inhibitor of depletion-stimulated calcium entry(Merritt et al. 1990 Biochem J. 271:515–522), had no effect oncapsaicin-evoked currents in VR1-expressing oocytes. Thus, VR1 does notappear to be a functional SOC under these circumstances.

Example 4 Sensory Neuron-Specific Expression of Capsaicin Receptor

The distribution of VR1 transcripts in neuronal and non-neural rattissues was assessed by both Northern blot and in situ hybridizationanalyses. Adult Sprague-Dawley rats were euthanized by asphyxiation inCO₂ and tissues freshly dissected. Poly A+ RNA was purified either bylysis in guanidinium isothiocyanate followed by purification on oligo-dTcellulose or with the FastTrack kit (Invitrogen). Approximately 2 μg ofeach sample was electrophoresed through a 0.8% agarose-formaldehyde gel,transferred to a nylon membrane (Hybond N, Amersham), and hybridizedwith a ³²P-labeled probe representing the entire VR1 cDNA. Blots werewashed at high stringency and autoradiographed. After probing withcapsaicin receptor cDNA, the same filters were reprobed with aradiolabeled cyclophilin cDNA fragment as a control (e.g., to correctfor relative RNA loading between samples).

For in situ hybridization histochemistry, adult female Sprague-Dawleyrats were anesthetized and perfused with 4% paraformaldehyde in PBS.Dorsal root ganglia, trigeminal ganglia and spinal cord were dissected,frozen in liquid N₂, embedded in OCT mounting medium, and sectioned on acryostat. Sections (15 micron) were processed and probed at 55° C.overnight with a digoxigenin-labeled cRNA generated by in vitrotranscription of a 1 kb fragment of the VR1 cDNA (nt 1513–2482) usingthe Genius kit (Boehringer Mannheim). Sections were developed withalkaline phosphatase-conjugated anti-digoxigenin Fab fragments accordingto the manufacturer's instructions.

Both Northern blot analysis and in situ hybridization histochemistryindicated that VR1 transcripts are expressed selectively within dorsalroot and trigeminal ganglia. An mRNA species of approximately 4 kb wasprominently expressed in trigeminal and dorsal root sensory ganglia,both of which have been shown to contain capsaicin-sensitive neurons.This transcript was absent from all other tissues examined, includingspinal cord and brain. A much smaller RNA species (approx. 1.5 kb) wasdetected in the kidney, but it is unclear whether this transcript couldencode a functional VR1 protein.

In situ hybridization to assess the cellular pattern of VR1 expressionwithin sensory ganglia showed that VR1 was expressed predominatelywithin a subset of neurons with small diameters within both dorsal rootand trigeminal ganglia. This is in keeping with the observation thatmost capsaicin-sensitive neurons have relatively small to medium-sizedcell bodies (Holzer 1991 Pharmacol. Rev. 43:143–201; Jansco et al. 1977Nature 270:741–743). In contrast to the predominant expression of VR1transcripts in neurons of the dorsal root ganglion, no visible signalwas observed in the adjacent spinal cord dorsal horn. While bindingsites for radiolabeled resiniferatoxin have been detected int eh dorsalhorn, these sites are believed to reside on presynaptic terminal thatproject from primary nociceptors located within adjacent dorsal rootganglia Holzer 1991, supra). The results here support thisinterpretation.

Example 5 Assessment of VR1 Pharmacology in Xenopus Oocytes

To compare the pharmacological properties of the cloned capsaicinreceptor to those of native vanilloid sites in sensory ganglia, VR1 wasexpression oocyte and used in whole-cell voltage clamp analysis toquantitatively examine its electrophysiological response to a variety ofvanilloid agonists (capsaicin, resiniferatoxin) and antagonists(capsazepine). VR1 was expressed in Xenopus oocytes as described above(Example 3), except that CaCl₂ (2 mM) was used in place of BaCl₂ whengenerating the capsazepine inhibition curve. The agonists capsaicin andresiniferatoxin were applied sequentially to the same Xenopus oocyteexpressing VR1. Membrane currents were recorded in the whole cellvoltage clamp configuration (V_(hold)=−40 mV).

The results of the capsaicin and resiniferatoxin studies are shown inFIGS. 10A–10B. Bars denote duration of agonist application. At negativeholding potentials, exposure to capsaicin or resiniferatoxin produceddose-dependent inward current responses in VR1 expressing oocytes, butnot in water-injected control cells. As observed in sensory neurons(Winter et al. 1990 Brain Res. 520:131–140; Liu et al. 1994 Proc. Natl.Acad. Sci. USA 91:738–741), capsaicin-evoked current responses returnedrapidly to baseline following agonist removal, whereas resiniferatoxinresponses often failed to recover, even after a prolonged washoutperiod. Half-maximal effective concentrations for these agonists werewithin an order of magnitude of those reported for native vanilloidreceptors (Oh et al., supra; Bevan et al. 1992 Br. J. Pharmacol.107:544–552), with resiniferatoxin being approximately 20-fold morepotent than capsaicin (EC₅₀=39.1 nM and 711.9 nM, respectively). Hillcoefficients derived from these analyses (1.95 and 2.08, respectively)suggest that full activation of the receptor involves the binding ofmore than one agonist molecule, again consistent with previouslydescribed properties of native vanilloid receptors (Oh et al., supra;Szallasi 1994 Gen. Pharmac. 25:223–243).

As shown in FIGS. 11A and 11B, capsaicin-evoked responses in VR1expressing oocytes were blocked by the competitive vanilloid receptorantagonist capsazepine at concentrations (IC₅₀=283.5 nM) that inhibitnative receptors (FIGS. 10A–10B). The current tracing shows that theblock of capsaicin activity (cap; 0.6 μM) by capzasepine (cpz; 10 μM) isreversible. Another pharmacological signature of vanilloid receptors istheir sensitivity to the non-competitive antagonist ruthenium red (RR;10 μM), which also blocked capsaicin-evoked responses (cap; 0.6 μM) in areversible manner (FIG. 11A). Responses to resiniferatoxin (50 nM) werealso reversibly antagonized by capsazepine (5 μM) or ruthenium red (10μM) (not shown).

Example 6 Patch Clamp Analysis of Recombinant Capsaicin ReceptorsExpressed in HEK293 Embryonal Kidney Cells

The recombinant capsaicin receptor cloned in Example 1 was furthercharacterized in studies using patch clamp analysis in capsaicinreceptor-expressing HEK293 cells. HEK293 cells transfected with acontrol vector (pcDNA3 without a capsaicin receptor-encoding sequence).Patch-amp recordings were carried out with transiently transfectedHEK293 cells at 22° C. Standard bath solution for whole-cell recordingscontained (mM) 140 NaCl, 5 KCl, 2 MgCl₂, 2 CaCl₂, 10 HEPES, 10 glucose,pH 7.4 (adjusted with NaOH). In calcium-free bath solution, CaCl₂ wasremoved and 5 mM EGTA was added.

For monovalent caution substitution experiments, after the whole-cellconfiguration was obtained in control bath solution, the bath solutionwas changed to (mM): 140 NaCl (or KCl or CsCl), 10 glucose, and 10 HEPES(adjusted to pH 7.4 with NaOH, KOH or CsOH, respectively) and thereversal potential measured using voltage-ramps. For divalent cationpermeability experiments, the bath solution was changed to (mM) 110MgCl₆ (or CaCl₂), 2 Mg(OH)₂ (or Ca(OH)₂), 10 glucose, 10 HEPES, pH 7.4(adjusted with HCl).

Bath solution for outside-out patch recordings and pipette solution forinside-out patch recordings contained (mM) 140 NaCl, 10 HEPES, pH 7.4(adjusted with NaOH). Bath solution for inside-out patch recordings andpipette solutions for outside-out patch recordings and ion substitutionexperiments contained: (mM) 140 NaCl, 10 HEPES, 5 EGTA, pH 7.4 (adjustedwith NaOH). Pipette solution for whole-cell recordings contained (mM)140 CsCl (or 130 CsAspartate and 10 NaCl), 5 EGTA, 10 HEPES, pH 7.4(adjusted with CsOH). Liquid junction potentials were measured directlyin separate experiments; they did not exceed 3 mV with solutions usedand no correction for this offset was made.

Whole-ell recording data were sampled at 20 kHz and filtered at 5 kHzfor analysis (Axopatch 200 amplifier with pCLAMP software, AxonInstruments). Single-channel recording data were sampled at 10 kHz andfiltered at 1 kHz. Permeability ratios for monovalent cations to Na(P_(x)/P_(Na)) were calculated as follows:P_(x)/P_(Na)=exp(ΔV_(rev)F/RT), where V_(rev) is the reversal potential,F is Faraday's constant, R is the universal gas constant, and T isabsolute temperature. For measurements of divalent permeability,P_(Y)/P_(Na) was calculated as follows: P_(Y)/P_(Na)=[Na⁺]₁exp(ΔV_(rev)F/RT)(1+exp(ΔV_(rev)F/RT))/4[Y²⁺]₀. Ion activitycoefficients of 0.75 (sodium) and 0.25 (calcium or magnesium) were usedas correction factors.

FIG. 3 show the results of whole cell voltage clamp analysis ofcapsaicin receptor-expressing HEK293 cells at −60 mV using aCsAsparate-filled pipet. These data show an inward cation-specificcurrent which is present only during capsaicin treatment (the timeperiod during which capsaicin was present (1 μM) is indicated by the barabove the plot), and which developed with a short latency upon bathapplication of capsaicin. No such currents were observed on control,mock-transfected cells. FIG. 4 shows the voltage steps (400 ms) from−100 mV to +40 mV (vertical lines in FIG. 3) on an expanded time scale.The currents in the absence of capsaicin (a) were subtracted mm thecurrents obtained in the presence of capsaicin (b). This analysis of thedata revealed a ime-independent, receptor-dependent current. Incalcium-free medium, the capsaicin-evoked current was alsotime-independent both at a constant holding potential of −60 mV (FIG. 3)and during voltage steps from −100 to +40 mV (in 20 mV increments, FIG.4). This property enabled characterization of capsaicin-mediatedcurrents under steady-states response conditions in subsequentexperiments. Current-voltage relations derived from these data show thatsuch responses exhibit prominent outward rectification resembling thatobserved in cultured dorsal root ganglion neurons (FIG. 4; Oh et al.,supra). Because the bath solution used in these experiments consistedmainly of sodium chloride, whereas the patch pipet was filled withcesium aspartate, the observed reversal potential close to 0 mV(E_(rev)=0.5±0.9 mV; n=13) indicates that the capsaicin-mediatedresponse involves the opening of a cation-selective channel.

In sensory neurons, vanilloid-evoked currents are carried by a mixtureof mono- and divalent cations (Bevan et al. 1990 Trends Pharmacol. Sci.11:330–333; Oh et al., supra; Wood et al. 1988 J. Neuroscience8:3208–3220). This phenomena was examined in VR1-expressing mammaliancells through a series of ion substitution experiments to examine therelative contributions of various cations to capsaicin-evoked currentsin VR1-expressing cells. Current-voltage relations established for cellsbathed in solutions of differing cationic compositions (FIG. 5; Na⁺(labeled a), K⁺ (labeled b), Cs⁺ (labeled c), Mg⁺⁺ (labeled d), or Ca⁺⁺(labeled e) revealed that VR1 does not discriminate among monovalentcations, but exhibits a notable preference for divalent cations.Replacement of extracellular NaCl (140 mM) with equimolar KCl or CsCldid not significantly shift reversal potential (E_(rev)=−0.7±1.2 mV,n=8; −1.5 mV, n=9; −4.3±0.9 mV, n=8, respectively. P_(K)/P_(Na)=0.94;P_(CS)/P_(Na)=0.85). Replacement of extracellular NaCl with isotonic(112 mM) MgCl₂ or CaCl₂ shifted E_(rev) to 14.4±1.3 mV (n=3) or 24.3±2.3mV (n=7), respectively. As summarized in FIG. 5, the data thus that thecapsaicin receptor-expressing cell membranes had the following relativecation permeabilities for the capsaicin-activated currentCa⁺⁺>Mg⁺⁺>>Na⁺=K⁺=Cs⁺. The very high relative permeability of VR1 tocalcium ions (P_(Ca)/P_(Na)=9.60; P_(Mg)/P_(Na)=4.99) exceeds thatobserved for most non-selective cation channels and is comparable tovalues reported for NMDA-type glutamate receptors (P_(Ca)/P_(Na)=10.6)(Mayer et al. 1987 J. Physiol. 394:501–527), which are noted for thisproperty. With alf bath solutions examined, an outwardly rectifyingcurrent-voltage relation was observed, although this feature wassomewhat less prominent in MgCl₂- or CaCl₂-containing bath solutions.

In cultured sensory neurons, electrophysiological analyses ofvanilloid-evoked responses have shown them to be kinetically complex andto desensitize with continuous vanilloid exposure (Liu et al., supra:Yeats et al. 1992 J. Physiol. 446:390P). This electrophysiologicaldesensitization (which might underlie aspects of physiologicaldesensitization produced by vanilloids in vivo) appears to depend, inpart, upon the presence of extracellular calcium (Yeats et al., supra;Holzer 1991 Pharmacol. Rev. 43:143–201). To test the calcium dependencyof VR1-expressing cells ability to respond to capsaicin, whole-cellcurrent responses were tested in both calcium-containing standard bathsolution and in calcium-free solution (FIGS. 6A–F). Capsaicin (1 μM) wasapplied every 5 min; CsCl was used as pipette solution. The ratios ofcurrent size at the end of the third application to the peak of thefirst application were 95.3±2.6% (n=3) in calcium-free solution, and13.0±4.3% (n=5) in calcium-containing solution (T test; p<0.00001).Indeed, in the absence of extracellular calcium, capsaicin-evokedresponses in VR1-transfected cells showed little or no desensitizationduring prolonged agonist application or with successive agonistchallenges (4.7±2.3% decrease between first and third applications,n=3). In contrast, responses evoked in calcium-containing bath solutionconsisted of at least two distinct components: one desensitizing(87±4.3% decrease between first and third applications, n=5); and onerelatively non-desensitizing. Thus, desensitization and multiphasickinetics of vanilloid-evoked responses can be reproduced outside of aneuronal context and distinguished by their dependence on ambientcalcium levels.

The behavior of the VR1 response was also examined in membrane patchesexcised from transfected cells. Inside-out (I/O) or outside-out (O/O)patches were excised from VR1-transfected cells and analyzed insymmetrical 140 mM NaCl at the indicated holding potentials withcapsaicin (1 μM) in the bath solution. Dashed lines in the datarepresented in FIG. 7 indicate closed channel state. In other patches,multiple simultaneous channel openings were observed. The large and wellresolved currents of unitary amplitude observed only in the presence ofcapsaicin (FIG. 7) indicate the existence of capsaicin-gated ionchannels within these patches, whose activation does not depend uponsoluble cytoplasmic components. The current voltage curve of mean singlechannel amplitudes (±s.e.m.; FIG. 8), which was calculated from datashown in FIG. 7, also exhibits pronounced outward rectification. Thecurrent-voltage relation at the single-channel level was essentiallyidentical to that established in whole-cell configuration, owing to itsoutward rectification and reversal potential near 0 mV under similarionic conditions. Unitary conductances of 76.7 pS at positive potentialsand 35.4 pS at negative potentials were observed with sodium as the solecharge carrier. These single channel properties mirror those previouslydescribed for native vanilloid receptors (Oh et al., supra; Forbes etal. 1988 Neurosci. Lett. Suppl. 32:S3).

It has been suggested that the site of vanilloid action may not beconfined to the extracellular side of the plasma membrane, reflectingthe lipophilic nature of these compounds (James et al. in Capsaicin inthe Study of Pain (ed. Wood) Pgs. 83–104 (Academic Press, London, 1993).Interestingly, capsaicin was able to produce identical responses whenadded to either side of a patch excised from a VR1-expressing cell (FIG.7), consistent with the notion that vanilloids can permeate or cross thelipid bilayer to mediate their effects. A less likely, but formallyconsistent explanation is that vanilloid receptors have functionallyequivalent capsaicin binding sites on both sides of the plasma membrane.

These data show that the cloned capsaicin receptor behaves in patchclamp analysis in a manner very similar to that reported for wildtypecapsaicin receptor.

Example 7 Use of Recombinant Capsaicin Receptor to Quantitate VanilloidConcentrations

As has been recognized for years, the relative pungencies of peppervarieties span an enormously wide range, reflecting, in part,differences in vanilloid content. To-date, methods for rating pepperswith respect to their relative “hotness” have relied on subjectivepsychophysical assays (in which values are reported in Scoville units)(Scoville 1912 J. Am. Pharm. Assoc. 1:453–454) or on biochemicaldetermination of capsaicin content (Woodbury 1980 J. Assoc. Off. Anal.Chem. 63:556–558). To further explore whether the electrophysiologicalresponse of the cloned vanilloid receptor to pepper extracts was inproportion to ability of these peppers to evoke pain.

Several different types of hot peppers (15 g; Thai green, poblano verde,habanero, and wax) were minced and extracted overnight at roomtemperature with 50 ml absolute ethanol. Soluble extracts wereconcentrated 15-fold by vacuum desiccation, then diluted 1000-fold infrog ringer's solution for electrophysiological assay. Equivalentfractions (normalized to pepper weight) were tested for their ability toactivate the recombinant capsaicin receptor expressed in Xenopusoocytes. Capsaicin receptor activation was assessed using atwo-electrode voltage-clamp assay to quantitatively measure currentselicited by each pepper extract. Responses were normalized to theresponse obtained with pure capsaicin (10 μM set at 100). The data areshown in FIG. 11 (each value represents an average of four independentdeterminations, each from separate oocytes; 30 sec application). Therelative response of the cloned receptor to the pepper samples and thecapsaicin control are shown in the histogram with representative currenttraces shown to the right of each bar in the histogram. Extracts evokedno response in water-injected cells.

The relative responses of capsaicin receptor to the pepper extractscorrelates with the relative hotness of each pepper as determined byconventional analyses and Scoville heat unit assignments. Moreover, thedifferential “hotness” of these pepper variants, as determined bysubjective psychophysical ratings (Berkeley et al. Peppers: A Cookbookpgs. 1–120 (Simon and Schuster, New York, 1992), correlated with theirrank order potencies as activators of VR1.

Example 8 Capsaicin Induces Death of Cells Expressing VR1

Capsaicin is widely recognized as a neurotoxin that selectively destroysprimary afferent nociceptors in vivo and in vitro (Jansco et al. 1977Nature 270:741–743; Wood et al. 1988 J. Neuroscience 8:3208–3220). Inorder to determine whether this selective toxicity solely is areflection of the specificity of receptor expression, or whether itdepends upon additional properties of sensory neurons or their milieu,the ability of capsaicin to kill non-neuronal cells expressing vanilloidreceptors was examined in vitro. HE293 cells were transientlytransfected with either vector alone (pcDNA3), vanilloid receptor cDNAdiluted 1:50 in pcDNA3 (VR1 1:50) or vanilloid receptor cDNA alone(VR1). Fourteen hours later, culture medium was replaced with mediumcontaining capsaicin (3 μM, filled bars) or vehicle (ethanol 0.3%, openbars) (FIG. 12). After seven hours at 37° C., the percentage of deadcells was determined using ethidium homodimer staining. Data representthe mean±s.e.m. of triplicate determinations from a representativeexperiment Asterisks indicate a significant difference fromethanol-treated cells (T-test, P<0.0001). Similar results were obtainedin three independent experiments.

As shown in FIG. 12, within several hours of continuous exposure tocapsaicin, HEK293 cells transfected with VR1 exhibited rampant death, asdetermined morphologically and by the use of vital stains. In contrast,cells transfected with vector alone were not killed by this treatment.The cell death was characterized by prominent cytoplasmic swelling,coalescence of cytoplasmic contents, and eventual lysis. Thus, VR1expression in a non-neuronal context can recapitulate the cytotoxicityobserved in vanilloid-treated sensory neurons. Staining with Hoechst dye33342 revealed no evidence of the nuclear fragmentation often associatedwith apoptotic cell death 28 (not shown). Together, these observationsare consistent with necrotic cell death resulting from excessive ioninflux, as has been proposed for vanilloid-induced death of nociceptors(Bevan et al. 1990 Trends Pharmacol. Sci. 11:330–333), glutamate-inducedexcitotoxicity (Choi 1994 Prog. Brain Res. 199:47–51), andneurodegeneration caused by constitutively activating mutations ofvarious ion channels (Hong et al. 1994 Nature 367:470–473; Hess 1996Neuron 16:1073–1076).

Example 9 Hydrogen Ions Potentiate the Effect of Capsaicin on VR1

A reduction in tissue pH resulting from infection, inflammation, orischemia can produce pain in mammals. This effect has been attributed tothe ability of protons to activate excitatory channels on the surface ofnociceptive neurons. A subset of these responses have been reported toshare properties in common with those elicited by vanilloids, includingsimilar kinetics, ion selectivity, and antagonism by ruthenium red(Bevan et al. 1994 Trends Neurosci. 17:509–512). Moreover, subthresholdconcentrations of hydrogen ions have been shown to potentiate theeffects of low concentrations of capsaicin in sensory neurons (Petersenet al. 1993 Pain 54:3742; Kress et al. 1996 Neurosci. Lett 211:58). Ithas therefore been proposed that protons might act as endogenousactivators or modulators of vanilloid receptors (Bevan et al. 1994supra).

To address this possibility, the effects of hydrogen ions on the clonedvanilloid receptor were examined using the oocyte expression system.Capsaicin (0.3 μM) was administered throughout the time period tested(spanned by the arrows in FIG. 13) (V_(hold)=−40 mV). The pH of the bathsolution was changed during the experiment (as indicated by thehorizontal bars in FIG. 13). VR1-expressing oocytes exhibited noresponses to pH 6.3 bath solution without capsaicin; water-injectedcontrol oocytes exhibited no responses, to either capsaicin or pH 6.3bath solution (not shown). The current responses obtained from 9independent VR1-expressing oocytes are summarized in FIG. 14. The greyportion of each bar indicates peak current evoked by capsaicin at pH7.6, while the black portion represents the additional current evoked bychanging the pH to 6.3.

Abrupt reduction in bath solution pH (from 7.6 to 5.5) was notsufficient to activate VR1 in the absence of capsaicin (fewer than 10%of VR1-expressing oocytes treated in this way exhibited a large inwardcurrent (not shown)), suggesting that hydrogen ions alone cannotefficiently activate this protein. Next, the effect of both capsaicinand pH on VR1 activation was examined. VR1-expressing oocytes weretreated with a submaximal concentration of capsaicin (500 nM) at pH 7.6(FIG. 13). Once their current responses reached a relativelystable-plateau, the oocytes were exposed to a solution containing thesame concentration of capsaicin at pH 6.3. Under these conditions, theinward current rapidly increased to a new plateau up to five-foldgreater in magnitude than the first. Upon returning to pH 7.6, theoocyte response subsided to its initial plateau, and upon the removal ofcapsaicin it returned to baseline. This potentiation was seen only withsub-saturating concentrations of agonist, as reduced pH did not augmentresponses to 10 μM capsaicin (not shown). These results suggest thatwhile hydrogen ions alone are not sufficient to activate VR1, they canmarkedly potentiate capsaicin-evoked responses.

Example 10 The Vanilloid Receptor is Activated by Noxious Heat

The effects of elevated temperature on VR1 activity in calcium influx,conductance, and capsaicin and RR responsivity were examined.

a) Effect of Heat Upon Intracellular Calcium

The effects of heat upon VR1 activity in mediating calcium influx wereexamined using transfected HEK293 cells and the flourescent calciuminflux screening method described above. Cells were analyzed usingmicroscopic fluorescent calcium imaging before and immediately after theaddition of heated calcium imaging buffer (300 ml CIB at 65° C. wasapplied to cells residing in 150 ml CIB at 22° C.) Under theseconditions, cells were transiently exposed to a peak temperature of −45°C.

While cells transfected with vector alone exhibited only a mild, diffusechange in cytoplasmic free calcium, a large proportion of cellsexpressing VR1 exhibited a pronounced elevation of calcium levels withinseconds of heat treatment. These responses subsided within a few minutesand a subsequent challenge with capsaicin produced a characteristiccalcium response, suggesting that the response to heat is a specificsignaling event and not a consequence of non-specific membraneperturbation or disruption to cell integrity.

b) Effect of Heat Upon Conductance

Whole-cell patch-clamp analysis (Vhold=−60 mV) of VR1-transfected HEK293cells was performed to examine whether specific heat-evoked membranecurrents are associated with this phenomenon. The temperature of thebath medium was raised from 22° C. to 48° C. (heat) and then restored to22° C., after which capsaicin (0.5 μM) was added to the bath. Ionicconditions were identical to those described for the data in FIG. 2.Voltage-ramps (−100 to +40 mV in 500 ms) were applied before, between,and during responses.

Exposure of these cells to a rapid increase in temperature (22° C. to50° C. in 25 seconds, monitored with an in-bath thermistor) producedlarge inward currents (791±235 pA at 60 mV; n=9) that were typicallysimilar in amplitude to that evoked by a subsequent application ofcapsaicin at 500 nM (FIG. 15A). Both heat- and vanilloid-evokedresponses showed outward rectification, suggesting that they aremediated by the same entity (FIG. 15B). By comparison, thermally-evokedresponses of control, vector-transfected cells were much smaller andexhibited no rectification (131±23 nA, n=8). In addition, the heatresponse in VR1-transfected cells desensitized during stimulusapplication, whereas the small thermal response observed in controlvector-transfected cells did not. These results suggest that VR1 isacting as a thermal transducer, either by itself or in conjunction withother cellular components.

c) Heat Activation of VR1 in Oocytes

To determine whether VR1 could mediate similar responses to heat in adifferent cellular environment, heat activation of VR1 was tested in theoocyte system. Oocytes injected with either VR1 cRNA or water weresubjected to two-electrode voltage-clamp (V_(hold)=−60 mV) while thetemperature of the perfusing buffer was raised from 22.7° C. to thelevel indicated, then held constant for 60 sec. The magnitudes of theresulting inward currents are shown in FIG. 16 as the mean±s.e.m. (VR1,n=8; water, n=6 independent cells). The asterisk indicates a significantdifference from water-injected oocytes (T-test, P<0.0005).

In control, water injected oocytes, acute elevation of perfusatetemperature produced a small inward current that increased linearly upto 50° C. (FIG. 16). VR1 expressing oocytes exhibited similar responsesat temperatures up to 40° C., but above this threshold, their responseswere significantly larger than those of controls. Thus, even in thisnon-mammalian context, the VR1-mediated temperature response profile isremarkably consistent with that reported for thermal nociceptors(Fields, supra).

d) Inhibition of VR1 Heat Activation by Ruthenium Red

To further determine whether heat acts specifically through thecapsaicin receptor, the ability of ruthenium red to inhibit theheat-mediated response was tested in VR1-expressing oocytes in thesystem described above. The current tracings shown in FIG. 17 weregenerated from representative VR1- or water-injected oocytes(V_(hold)=−60 mV) during successive applications of the indicatedstimuli.

VR1-injected oocytes exhibited the following mean inward currentresponses±s.e.m. (n=5): capsaicin (1 μM), 1221±148 nA; heat (50° C.),2009±134 nA; heat plus ruthenium red (10 μM), 243±47 nA. Inhibition byruthenium red was significant (88±2%, n=5; Paired T-test, P<0.0001). Nodiminution in current response was observed when successive heat pulseswere administered in the absence of ruthenium red. Water-injectedoocytes showed no response to capsaicin and much smaller responses toheat (338±101 nA, n=5). Ruthenium red inhibited these responses by only21±26% (n=5; Paired T-test, P<0.1).

These data indicate that VR1 is directly involved in this thermalresponse; application of ruthenium red reduced significantly (88±2%;n=5) the response of VR1-expressing oocytes to heat, while the smallerresponse seen in control cells was reduced by only 21±26% (n=5) (FIG.17). Taken together, these observations strongly support the hypothesisthat VR1 is activated by noxious, but not innocuous heat.

Example 11 Chromosomal Localization and Isolation of the Mouse VR1 Gene

The chromosomal localization of the mouse VR1 gene was determined usingfluorescent in situ hybridization (FISH) according to methods well knownin the art. Briefly, a bacterial artificial chromosome containing a90–100 kb insert of mouse genomic DNA encoding portions of the mouse VR1gene was isolated by PCR analysis and Southern hybridization using ratVR1-derived probes. This insert was labeled with digoxigenin and appliedto metaphase spreads of mouse chromosomes. Fluorescently taggedanti-digoxigenin antibodies were then used to visualize the position onthe chromosomes to which the VR1 gene hybridized.

The VR1 gene mapped to the B3 band of mouse chromosome 11, approximately49% of the way from the heterochromatic-euchromatic boundary to thetelomere of chromosome 11. This region of the mouse chromosome issyntenic to human chromosome 17, particularly the regions 17p11-13,17pter, and 17qter. It is therefore probable that the human VR1 gene islocated within those analogous regions on the human chromosome.

The mouse VR1 gene was sequenced according to methods well known in theart The nucleotide (SEQ ID NO:10) and amino acid (SEQ ID NO:11)sequences of mouse VR1 are provided in the Sequence Listing below. Therat and mouse VR1 amino acid sequences are more than 95% identical.

Example 12 Identification of Capsaicin Receptor-Related PolypeptideVRRP-1

A Genbank database search using VR1 revealed a number of human and mouseEST sequences similar VR1. Alignment of these EST sequences suggestedthat all of them, except one (see below) encode identical or verysimilar genes, suggesting that they represent fragments of the human andmouse versions of the VR1 gene. Over all regions analyzed, the predictedsequences of the encoded human and mouse proteins were highly identicalto one another, but only about 50% identical to the rat VR1. Becausemouse VR1 protein is more similar to the rat VR1 protein than 50%, weconcluded that these EST sequences must encode human and mouse versionsof a related protein, which we have termed VRRP-1. VRRP-1 is an exampleof the capsaicin receptor-related polypeptides encompassed by thepresent invention.

Portions of the VRRP-1 genes from mouse brain, rat brain, and humanCCRF-CEM cells were cloned using PCR primers (GAC CAG CAA GTA CCT CAC(SEQ ID NO:12) and C TCC CAT GCA GCC CAG. TTT ACT TCC TCC ACC CTG AAGCAC CAG CGC TCA (SEQ ID NO:13))), which were based on the consensus ofhuman and mouse EST sequences. A full-length rat VRRP-1 cDNA wasisolated from a rat brain cDNA library using the rat PCR product as aradiolabeled probe. The rat VRRP-1 cDNA (SEQ ID NO:3; amino acidsequence SEQ ID NO:4)) is approximately 49% identical to rat VR1 at theamino acid level (SEQ ID NOS:2 (rat VR1) and 4 (rat VRRP-1)) and 59%identical at the nucleotide level (SEQ ID NOS:1 (rat VR1) and 3 (ratVRRP-1)).

VRRP-1 does not appear to be activated by capsaicin or heat Preliminaryevidence suggests VRRP-1 may interact with VR1.

Example 13 Identification of Human Capsaicin Receptor VR1

Comparison of VR1 with VRRP-1 and other sequences in the Genbankdatabase suggested that VR1 and VRRP-1 are much more closely related toone another than to any other cloned sequences, with one exception. Asingle human EST sequence (accession number AA321554; SEQ ID NO:8)obtained from human CCRF-CEM lymphoid cells encodes an amino acidsequence (SEQ ID NO:9) that is at least 71% identical and at least 80%similar to the predicted extreme carboxy terminal domain of the rat VR1(amino acid residues 774 to 838 of SEQ ID NO:2; see Region 2 of theschematic in FIG. 18). Moreover, rat VR1 (SEQ ID NO:1) and the human ESTAA321554 (SEQ ID NO:8) are 75% identical at the nucleotide level. Inaddition, EST AA321554 contains a stop codon in the same position as thestop codon in rat VR1. In contrast although there is homology between aportion of EST M321554 and the carboxy terminus of rat VRRP-1 (seeRegion 1 in FIG. 18), the rat VRRP-1 polypeptide is shorter than the ratVR1 polypeptide and the protein from wich EST AA321554 appears to bederived. Moreover, even with in Region 1, there is greater homologybetween rat VR1 and EST AA321554 than between either rat VR1 and ratVRRP-1 or than between rat VRRP-1 and EST M321554. Therefore, the humanEST sequence AA321554 represents the human version (ortholog) of ratVR1.

PCR primers based upon the human sequence were designed to amplify thisfragment from cDNA isolated from CCRF-CEM cells or from human sensoryganglion cDNA. The resulting fragment is used as a probe to screen ahuman genomic DNA library to obtain a full-length human VR1 cDNAsequence from CCRF-CEM cell or human sensory ganglion cDNA. Using theresulting human VR1 genomic fragment, the chromosomal localization ofthe VR1 gene is confirmed by FISH. The function of the polypeptideencoded by the human VR1 gene is confirmed using the functional assaysdescribed above.

Example 14 Identification of Human Capsaicin Receptor-RelatedPolypeptide VRRP-1

Rat VRRP-1 sequences were used to screen the Genbank database toidentify capsaicin receptor-related polypeptides from other organisms.The screen identified several human and mouse EST sequences havinghomology to three separate regions of rat VRRP-1, which regions aretermed Regions A, B, and C. Regions A, B, and C represents portions ofthe VRRP-1 sequence within which the human and mouse VRRP-1-encodingESTs are clustered, listed from 5′ to 3′ respectively. Region Aencompasses from about residue 580 to about residue 850; Region Bencompasses from about nucleotide residue 960 to about residue 1730; andRegion C encompasses from about nucleotide residue 1820 to about residue2505 in rat the VRRP-1 nucleotide sequence. A summary of the human andmouse EST sequences corresponding to each of these regions is providedin the table below.

TABLE Human and Mouse EST Sequences Corresponding to Rat VRRP-1 RatVRRP-1 Region B Rat VRRP-1 Region C Rat VRRP-1 Region A (GenbankAccession (Genbank Accession (Genbank Accession Nos.) Nos.) Nos.) HumanH20025, AA236416, H51393, AA281349, W44731, W92895, T12251, ESTsAA236417, H27879, H50364, N23395, W38665, AA304033, N35179, N21167,AA461295, N26729, AA357145, N24224 AA281348 H21490, H49060 Mouse W82502,W53556 AA139413 AA476107, AA015295, ESTs AA274980

These human and mouse EST sequences can be used to determine a consensusnucleotide sequence for each of Regions A, B, and C. The consensusnucleotide sequence for human VRRP-1 for Region A (SEQ ID NO:5), RegionB (SEQ ID NO:6), and Region C (SEQ ID NO:7) are provided in the SequenceListing below. The consensus sequences can be used to design PCR probesto isolate a fragment encoding the full-length VRRP-1 using methods thatare well known in the art.

Example 15 Cloning and Sequencing of a Human VRRP-1

The rat VR1 nucleotide and protein sequences were used to search thegenbank databases for related entities. A number of expressed sequencetag (EST) sequences were found that exhibited homology to the rat VR1.These were from human and mouse sources. These sequences were alignedwith each other and with rat VR1 and found that all but one of the humansequences appeared to encode the same protein and that this protein washighly homologous to the protein encoded by the mouse sequences. Thepredicted sequences of these human and mouse proteins were about 50%identical to the rat VR1 protein but much more hightly related to oneanother.

Using the human and mouse EST sequences, PCR primers were designed thatwere then used on rat brain-derived cDNA to amplify a DNA fragmentencoding most of this putative protein. This fragment was radiolabeledand used as a hybridization probe to isolate a full-length cDNA from arat brain-derived cDNA library. The cDNA (rat VRRP-1) encodes a proteinof 761 aa (SEQ ID NO:3) that is 49% identical to the rat VR1 protein and74% identical to the human VRRP1 protein (SEQ ID NO:23) predicted fromthe available EST sequences. The rat VRRP-1 mRNA is expressed in sensoryganglia and in other tissues such as brain, spinal cord, spleen, lung,and large intestine.

The human and mouse EST sequences were used to design PCR primers thatwould allow amplification of the human VRRP-1 sequence from ahuman-derived cDNA source. Using cDNA derived from human CCRF-CEM cells,a fragment of the human VRRP-1 cDNA was amplified and sequenced, therebyconfirming its identity with a subset of the reported EST sequences.Subsequently, PCR primers directed against the 5 prime and 3 prime endsof the predicted human VRRP-1 sequence were used to amplify fromCCRF-CEM-derived cDNA a DNA band of approximately 2500 bp, which is thecorrect size for the human cDNA, as predicted by the alignment of thehuman EST sequences with the rat VRRP-1. The human cDNA was thensequenced using standard methods well known in the art. The DNA sequenceof human VRRP-1 (VR2) is provided as SEQ ID NO:35, with the deducedamino acid sequence provided as SEQ ID NO:36.

Example 16 Cloning Chicken VR1 Homologues

Degenerate oligonucleotides were designed based on the amino acidsequence of rat VR1. The oligonucleotides ODJ3885 and ODJ3887corresponding to VR1 amino acid residues 63844 and 676–682,respectively, were used as primers for polymerase chain reactions (PCR)with chick genomic DNA as template.

ODJ3885 (SEQ ID NO:28)- 5′ TT(TC) AA(AG) TT(TC) AC(GATC) AT(ATC)GG(GATC) ATG ODJ3887 (SEQ ID NO:29) 5′ CAT(GATC)A(GA)(GATC)GC(GAT)AT(GATC)A(GA)CAT(AG)TT

Products of approximately 130 bp resulted, which were isolated andligated into the vector pT-Adv (Clontech). The inserts in several ofthese plasmid clones were sequenced. The products from chick genomic DNAfell into two classes: one also corresponding to a very dose homologue,and another corresponding to a somewhat more divergent homologue.

CVR-PCR1 (SEQ ID NO:30) TTCAAGTTCACGATTGGGATGGGTGACCTGGATTTTCATGAACATGCCAGATTCAGATACTTTGTCATGCTTCTGCTGCTGCTTTTTGTGATCCTCACCTACATCCTT TTGCTCAACATGCTTATAGCCCTTATACVR-PCR2 (SEQ ID NO:31) TTCAAGTTCACTATTGGGATGGGAGACCTGGAGTTTACAGAGAACTACAGGTTCAAGTCTGTGTTTGTCATCCTTTTGGTTCTCTATGTCATCCTTACGTACATCCTC CTGCTCAATATGCTTATAGCCCTAATG

A 150 bp EcoRI fragment containing CVR-PCR2 was used as a hybridizationprobe to screen clones from a cDNA library derived from RNA isolatedfrom chick embryonic dorsal root ganglia (DRG). Several hybridizingplasmids were identified Two of these correspond to a probable chickorthologue of rat VR1. The insert of one of these pCVR2 was sequenced inits entirety (SEQ ID NO:24). The deduced protein sequence (SEQ ID NO:25)shows an amino add identity to rat VR1 of 67%. Nucleotide alignment ofthe coding regions of rat and chick VR1 cDNAs also shows 67% identity.Electrophysiological and calcium-imaging analysis of HEK293 cellstransfected with pCVR2 indicate that the encoded protein responds toprotons and to high doses of the vanilloid, resiniferatoxin, but not tocapsaicin and to heating protocols which activate rat VR1.

Example 17 Cloning of a Human Vanilloid Receptor

A PCR reaction using ODJ3885 and ODJ3887 with human genomic DNA astemplate produced a 130 bp product. This band was purified and clonedinto pT-Adv. The inserts of several clones were sequenced, which showedthem all to encode a very close homologue or othologue of rat VR1. Thenucleotide sequence (SEQ ID NO:26) is 91% identical to the correspondingregion of rat VR1. The deduced protein sequence over this 45 codonsegement is identical to that of rat VR1.

Using this new alignment, additional PCR primers were designed to allowamplification of larger segments of VR1-homologous sequences from humancDNA sources. Primers ODJ4018, corresponding to VR1 amino acid residues423–429, and ODJ3767, which was derived from the sequence of human ESTAA321554, were used in a PCR reaction using as template cDNA from humanDRG.

ODJ4018 (SEQ ID NO:31) 5′ TA(TC) TT(TC) AA(TC) TT(TC) TT(TC) GT(GATC) TA3′ ODJ3767 (SEQ ID NO:32) 5′ AAA AGG GGG ACC AGG GC 3′

The resulting products were separated by gel electrophoresis transferredto nylon membranes for hybridization with a 150 bp probe derived fromthe previous PCR anlysis. A hybridizing fragment of about 1100 bp wasthus identified. This is the size expected to be produced by the posbonof these primers in the rat VR1 sequence.

The fragment is cloned for sequence analysis. The resulting sequencedata is used to design primers for cloning a full length human cDNAcorresponding to this sequence. This will be accomplished using the RACEPCR cloning method [Frohman, M. A. (1993) Methods Enzymol,218:340–358.]. This may also be carried out using primers derived fromthe sequence of the small PCR fragment HVR-PCR1.

Example 18 Cloning and Sequencing of a Human Vanilloid Receptor (VR1)

In order to obtain sequences corresponding to the human orthologue ofrat VR1, a segment of human genomic DNA was identified which containedsequences present in hVR-PCR1. This genomic DNA was isolated from alibrary of BAC plasmid clones containing large segments of human genomicDNA (Shizuya, et al 1992, Proc Nat Acad of Sci USA, 89:8794–8797) byGenomic Systems Inc., using oligonucleotide PCR primers derived from thesequence determined for hVR-PCR1.=PCR reactions using oligonucleotidesODJ4079 (GGCGACCTGGAGTTCACTGAG (SEQ ID NO:37)) and ODJ4080(GAGCAGGAGGATGTAGGTGAG (SEQ ID NO:38)) as primers, and human genomic DNAas template resulted in the expected 92 bp product A product of the samesize was also obtained using as-template cDNA from CCRF-CEM, a humancell line from which the EST sequence #24046 was obtained. This ESTsequence appeared to correspond to a close homologue or orthologue ofrat VR1. Using these primers to screen a human BAC library by PCR,Genomes Systems provided two BAC plasmid clones, 20614 and 20615.

These two clones were further analyzed by restriction digestion andSouthern blotting, using the VR1 hybridization probes described above.Inspection of the pattern of restriction fragments using severaldifferent restriction endonucleases indicated that these two clones wereprobably identical. In order to confirm that these plasmids, in fact,contained VR1-related sequences, Southern blots from these digests werehybridized incubated with different VR1 hybridization probes. The blotswere first hybridized to a ³²P labeled 150 bp EcoRI fragment fromhVR-PCR1. A single fragment from each digest hybridized with this probe.

In the case of a PstI digest the hybridizing fragment was approximately250 bp. The products of PstI digestion of this BAC plasmid were ligatedinto PstI-digested pBluescriptSK+. The resulting ligation products wereused to transform cells of the E. coli strain DH5α. Resultingtransformants were screened by hybridization with the same hVR-PCR1probe. The insert of one of these clones, hVR1-P1 was sequenced. Theresults showed that it was highly similar to rat VR1 and corresponded tohVR-PCR1. Alignment of the exon portion of this insert with rVR1 cDNA isshown below.

In order to further localize VR1-related sequences on this BAC plasmidinsert, Southern blots were performed using a 1008 bp NheI fragment fromthe rVR1 cDNA as a hybridization probe. This fragment includes almostthe entire 5′ portion of the rVR1 coding sequence. In this case eachdigest produced one or more fragments that hybridized strongly with thisprobe. In particular, HindIII digestion produced two hybridizingfragments of approximately 12 kbp and 18 kbp. The 18 kbp also hybridizedwith the hVR-PCR1 probe, indicating that the 12 kbp fragment probablycontained the 5′ end of the hVR1-coding region. These fragments weresubcloned into pBluescriptSK+ for further analysis. Three resultingclones were obtained. The clones hVR1-H1 and hVR1-H2 contained the 12kbp fragment inserted in opposite-orientations. The clone hVR1-H3,contained a 18 kbp insert. Sequence reactions carried out usingvector-derived primers resulted in no VR1-related sequences, indicatingthat these end segments corresponded to either introns or 5′ or 3′flanking sequences. A sequencing reaction of hVR1-H3 using the primerCCRF2, which was derived from the EST24046 sequence was also carriedout. The resulting sequence data showed that hVR1-H3 containedVR1-related sequence that appeared to be identical to that present inEST24046. An alignment of these two sequences is shown below.

In order to identify sequences at the 5′ end of the human VR1 codingregion present in this genomic clone, a 1500 bp BamHI fragment wassubcloned from hVR1-H1 into pBluescriptSK+. The insert in one of theresulting clones, hVR1-B2 was sequenced using vector-based primers (T3and T7). Sequence from one end of this clone revealed VR1-relatedsequence as shown by the nucleotide alignment or by alignment of thededuced protein sequence of this clone with that of rVR1. Inspection ofthese alignments shown below indicated that the translational start ofthe hVR1 coding region is probably at position 14 of this sequence.

Using this sequence information, two primers were designed to allowproduction of a human VR1 cDNA from using RT-PCR from polyA+ RNAisolated from the CCRF-CEM cell line. The two primers ODJ4157.(AGAAATGGAGCAGCACAGACTTGG (SEQ ID NO:47)) and ODJ4162(TCACTTCTCCCCGGAAGCGGCAG (SEQ ID NO:48)) were used as primers in a PCRreaction with CCRF-CEM cDNA as template. A product of about 2500 bpresulted from this reaction. Southern blot analysis of this productusing a hVR-PCR1 hybridization probe, indicated that this product was,in fact, VR1-related. The product was purified by preparative agarosegel electrophoresis and subcloned into the vector pT-Adv (Clontech).Several clones were isolated and four of these were subjected to DNAsequence analysis. The resulting DNA sequence of human VR1 is providedas SEQ ID NO:33, with the deduced amino acid sequence provided as SEQ IDNO:34.

All publications and patents mentioned in the above specification areherein incorporated by reference. Various modifications and variationsof the described method and system of the invention will be apparent tothose skilled in the art without departing from the scope and spirit ofthe invention. Although the invention has been described in connectionwith specific preferred embodiments, it should be understood that theinvention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes forcarrying out the invention which are obvious to those skilled inmolecular biology or related fields are intended to be within the scopeof the following claims.

Before the present nucleotide and polypeptide sequences are described,it is to be understood that this invention is not limited to theparticular methodology, protocols, cell lines, vectors and reagentsdescribed as such may, of course, vary. It is also to be understood thatthe terminology used herein is for the purpose of describing particularembodiments only, and is not intended to limit the scope of the presentinvention which will be limited only by the appended claims.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “and”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “ahost cell” includes a plurality of such host cells and reference to “theantbody” includes reference to one or more antibodies and equivalentsthereof known to those skilled in the art, and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this invention belongs. Although any methods, devicesand materials similar or equivalent to those described herein can beused in the practice or testing of the invention, the preferred methods,devices and materials are now described.

All publications mentioned herein are incorporated herein by referencefor the purpose of describing and disclosing, for example, the celllines, vectors, and methodologies which are described in thepublications which might be used in connection with the presentlydescribed invention. The publications discussed herein are providedsolely for their disclosure prior to the filing date of the presentapplication. Nothing herein is to be construed as an admission that theinventors are not entitled to antedate such disclosure by virtue ofprior invention.

1. A method of screening for an agent that modulates capsaicin receptorfunction, the method comprising: a) combining a candidate agent with aeukaryotic cell comprising a recombinant nucleic acid, wherein therecombinant nucleic acid comprises a nucleotide sequence that encodes abiologically active capsaicin receptor polypeptide, which nucleotidesequence is operably linked to a promoter, wherein said capsaicinreceptor is encoded by a polynucleotide that hybridizes under stringenthybridization conditions to the complement of a polynucleotide having anucleotide sequence selected from SEQ ID NO:10, SEQ ID NO:24, and SEQ IDNO:33, and wherein the capsaicin receptor polypeptide is expressed onthe cell surface; and b) determining the effect of said agent oncapsaicin receptor function.
 2. The method of claim 1, wherein saiddetermining is by measuring capsaicin receptor-mediated increase inintracellular concentration of a cation.
 3. The method of claim 2,wherein the cation is selected from calcium, magnesium, potassium,cesium, and sodium.
 4. The method of claim 2, wherein the cation iscalcium.
 5. The method of claim 1, wherein said determining is bymeasuring a capsaicin receptor-mediated electrophysiological response.6. The method of claim 5, wherein the electrophysiological response isan inward cation-specific current.
 7. The method of claim 5, wherein theresponse is measured using a fluorescent voltage-sensitive dye.
 8. Themethod of claim 1, wherein said determining is by measuring blocking theactivity of a capsaicin receptor antagonist.
 9. The method of claim 8,wherein the capsaicin receptor antagonist is selected from the groupconsisting of capsazepine and ruthenium red.
 10. The method of claim 1,wherein said determining is by measuring blocking the activity of acapsaicin receptor agonist.
 11. The method of claim 10, wherein thecapsaicin receptor agonist is selected from resiniferatoxin andcapsaicin.
 12. The method of claim 1, wherein said determining is bymeasuring capsaicin receptor-mediated apoptosis.
 13. The method of claim1, wherein said cell further comprises a reporter gene operably linkedto a calcium inducible promoter, and wherein said determining is bymeasuring calcium-induced expression of the reporter gene.
 14. Themethod of claim 1, wherein the cell is selected from an amphibianoocyte, a mammalian cell line, and a cultured neuron.
 15. The method ofclaim 1, wherein the capsaicin receptor is a mammalian capsaicinreceptor.